Franciszek Janowiak

Importance of abscisic acid for chilling tolerance of maize seedlings

Summary A hypothesis developed in two earlier papers (Capell and Dorffling 1993, Janowiak and Dorffling 1996), but critically reinvestigated recently by Ristic et al. 1998 was tested again with new material and methods. According to the hypothesis, chilling tolerant maize genotypes accumulate abscisic acid (ABA) faster and in higher amounts than chilling sensitive genotypes when exposed to chilling stress. This relationship is in accordance with a suggested protective role of ABA against chilling injury. The hypothesis was tested in two ways: first by investigating 20 new maize genotypes with defined differences in chilling tolerance, second by manipulating the endogenous level of ABA during a low temperature treatment by applying the ABA biosynthesis inhibitor norflurazon and measuring the resulting chilling tolerance. Results of the first approach showed that the accumulation of ABA in the third leaves determined by an indirect ELISA after two days of chilling at 4 °C was significantly correlated with chilling tolerance as measured by necrotic injury and by ϕ PSII of the 20 tested genotypes. Accumulation of ABA induced by low temperature was significantly higher in the group of chilling tolerant genotypes than in that of chilling sensitive ones. It was inversely related to chilling-induced water loss. Results of the second experiment showed that norflurazon-treated seedlings were less chilling tolerant and accumulated less ABA than untreated ones. Application of ABA compensated the reduction in chilling tolerance by norflurazon. It is concluded that the results support the above mentioned hypothesis that chilling tolerance in maize is related to the ability to accumulate ABA as a protective agent against chilling injury.

Ionic and pH signalling from roots to shoots of flooded tomato plants in relation to stomatal closure

Soil flooding damages shoot systems by inhibiting root functioning. An example is the inhibition of water uptake brought about by decreased root hydraulic conductance. The extent of any resulting foliar dehydration this causes is limited by partial stomatal closure that begins within 4 h and is maintained for several days. Root to shoot signals that promote closure in flooded tomato plants have remained elusive but may include changes in solute delivery to the shoot by transpiration. Accordingly, we examined total osmolites and selected mineral ions in samples of xylem sap flowing at rates approximating whole plant transpiration. After 2.5 h flooding,delivery of total osmolites and of PO43-SO42-Ca2+K+NO3− and H+strongly decreased while Na+ remained excluded. Several hours later, deliveries of osmolites, PO43-, SO42-, Ca2+, and Na+ rose above control values, suggesting that, after approximately 10 h, root integrity became degraded and solute uptake de-regulated. Deliveries of NO3− remained below control values. Reducing or eliminating the supply of K+ to detached leaves to test the potential of decreased K+ delivery to close stomata proved negative. Decrease in H+ delivery was associated with sap alkalisation. However, raising the pH of buffer from 6.0 or 6.5 to 7.0 did not close stomata when tested in the presence of abscisic acid (ABA) at a concentration (10 μmol m−3) typical of the transpiration stream of flooded plants. It is concluded that despite their rapidity and scale, negative messages in the form of increased pH and decreased solute delivery from roots to shoots are, themselves, unlikely initiators of stomatal closure in flooded tomato plants.

A Specialized Histone H1 Variant Is Required for Adaptive Responses to Complex Abiotic Stress and Related DNA Methylation in Arabidopsis

Stress-inducible linker histone variant is required for adaptive response of Arabidopsis to complex environmental stress. Linker (H1) histones play critical roles in chromatin compaction in higher eukaryotes. They are also the most variable of the histones, with numerous nonallelic variants cooccurring in the same cell. Plants contain a distinct subclass of minor H1 variants that are induced by drought and abscisic acid and have been implicated in mediating adaptive responses to stress. However, how these variants facilitate adaptation remains poorly understood. Here, we show that the single Arabidopsis (Arabidopsis thaliana) stress-inducible variant H1.3 occurs in plants in two separate and most likely autonomous pools: a constitutive guard cell-specific pool and a facultative environmentally controlled pool localized in other tissues. Physiological and transcriptomic analyses of h1.3 null mutants demonstrate that H1.3 is required for both proper stomatal functioning under normal growth conditions and adaptive developmental responses to combined light and water deficiency. Using fluorescence recovery after photobleaching analysis, we show that H1.3 has superfast chromatin dynamics, and in contrast to the main Arabidopsis H1 variants H1.1 and H1.2, it has no stable bound fraction. The results of global occupancy studies demonstrate that, while H1.3 has the same overall binding properties as the main H1 variants, including predominant heterochromatin localization, it differs from them in its preferences for chromatin regions with epigenetic signatures of active and repressed transcription. We also show that H1.3 is required for a substantial part of DNA methylation associated with environmental stress, suggesting that the likely mechanism underlying H1.3 function may be the facilitation of chromatin accessibility by direct competition with the main H1 variants.

Alleviation of Osmotic Stress Effects by Exogenous Application of Salicylic or Abscisic Acid on Wheat Seedlings

The aim of the study was to assess the role of salicylic acid (SA) and abscisic acid (ABA) in osmotic stress tolerance of wheat seedlings. This was accomplished by determining the impact of the acids applied exogenously on seedlings grown under osmotic stress in hydroponics. The investigation was unique in its comprehensiveness, examining changes under osmotic stress and other conditions, and testing a number of parameters simultaneously. In both drought susceptible (SQ1) and drought resistant (CS) wheat cultivars, significant physiological and biochemical changes were observed upon the addition of SA (0.05 mM) or ABA (0.1 μM) to solutions containing half-strength Hoagland medium and PEG 6000 (−0.75 MPa). The most noticeable result of supplementing SA or ABA to the medium (PEG + SA and PEG + ABA) was a decrease in the length of leaves and roots in both cultivars. While PEG treatment reduced gas exchange parameters, chlorophyll content in CS, and osmotic potential, and conversely, increased lipid peroxidation, soluble carbohydrates in SQ1, proline content in both cultivars and total antioxidants activity in SQ1, PEG + SA or PEG + ABA did not change the values of these parameters. Furthermore, PEG caused a two-fold increase of endogenous ABA content in SQ1 and a four-fold increase in CS. PEG + ABA increased endogenous ABA only in SQ1, whereas PEG + SA caused a greater increase of ABA content in both cultivars compared to PEG. In PEG-treated plants growing until the harvest, a greater decrease of yield components was observed in SQ1 than in CS. PEG + SA, and particularly PEG + ABA, caused a greater increase of these yield parameters in CS compared to SQ1. In conclusion, SA and ABA ameliorate, particularly in the tolerant wheat cultivar, the harmful effects and after effects of osmotic stress induced by PEG in hydroponics through better osmotic adjustment achieved by an increase in proline and carbohydrate content as well as by an increase in antioxidant activity.

Chilling of maize seedlings : Changes in water status and abscisic acid content in ten genotypes differing in chilling tolerance

Summary The objective of the present paper was to study the relationship between chilling tolerance and chilling-induced abscisic acid (ABA) accumulation in maize. Ten maize genotypes, five classified as chilling tolerant and five as chilling sensitive, were used. Two of them, Co 125 and F 7, with significant differences in chilling tolerance, were studied in detail. Seedlings at the third leaf stage, without and with previous acclimation, were chilled at 5 °C and at relative humidities (RH) of 65 and 100%. Immediately before and during chilling the ABA content in the third leaf was measured by RIA. Water content, osmotic potential, and - after recovery - the degree of necrotic injuries were also determined. Chilling of non-acclimated seedlings at 65 % RH caused accumulation of ABA in all ten genotypes. The ABA accumulation was significantly higher in the chilling tolerant genotypes than in the chilling sensitive ones. Chilling of non-acclimated seedlings at 100% RH, studied in the two inbreds, caused ABA accumulation only in the chilling tolerant inbred F 7, although there were no significant changes in the water relations. Acclimation ( 4 days at 14/12 °C, 70% RH) had only marginal influence on the ABA content but increased the chilling tolerance markedly. The higher chilling tolerance of acclimated seedlings was accompanied by the ability for greater ABA accumulation during chilling, especially in the chilling tolerantinbred F 7. Thresholds of water content and osmotic potential for the rise of ABA were higher in tolerant than in sensitive genotypes. It is suggested that higher chilling tolerance is related to the ability for greater and faster ABA accumulation and better stabilization of water status in response to chilling. Evidence is presented that the rise in ABA is induced indirectly by chilling-induced water deficit as well as directly by the chilling temperature.

Stress-induced changes important for effective androgenic induction in isolated microspore culture of triticale (× Triticosecale Wittm.)

The accumulation of abscisic acid (ABA) and the activities of antioxidative enzymes along with cell metabolic activity were monitored during androgenesis induction in triticale (×Triticosecale Wittm.). Tested cultivars ‘Mieszko’ and ‘Wanad’ were selected due to their significantly different responses to androgenic induction. Significant variation was observed in respect of superoxide dismutase activity and endogenous ABA content in anthers isolated from freshly cut tillers. For both cultivars, tillers pretreatment with low temperature decreased peroxidase activity by 36%, highly accelerated respiration rate and reduced heat production. At the same time, the level of ABA in ‘Mieszko’ was increased to the level measured in ‘Wanad’. This effect was associated with higher microspore culture viability and increased stress tolerance in ‘Mieszko’. Low temperature and metabolic starvation during 4-day anther preculture did not influence activities of antioxidative enzymes, while it resulted in slight decrease in respiration rate and heat emission. The importance of these changes for effective androgenesis induction is discussed.

The initiation of elongation growth during long-term low-temperature stay of spring-type oilseed rape may trigger loss of frost resistance and changes in photosynthetic apparatus

The aim of the present investigation was to determine if the loss of frost resistance observed in spring-type oilseed rape during winter may be the effect of the tendency to start elongation growth during the prolonged low-temperature stay. Interactions between elongation growth rate, properties of photosynthetic apparatus and frost resistance were studied under these conditions in spring and winter cultivars of oilseed rape. Both spring and winter cultivars of oilseed rape reached the maximal frost resistance after 6 weeks at +5 degrees C. Photosynthetic apparatus of both cultivars acclimated to functioning in cold. The resistance of winter type plants remained unchanged at the end of the experiment (10 weeks) whereas spring-type plants lost the maximal resistance in subsequent weeks. It was preceded in the 7th week of low-temperature stay by acceleration of elongation growth without an increase in dry matter accumulation. A gradual loss of photosynthetic activity was also observed during this period. It was manifested as a decrease in antenna trapping efficiency, photochemical and non-photochemical fluorescence quenching and actual quantum yield of PSII without affecting apparent quantum yield of PSII. At the 70th day of the experiment, a decrease in CO(2) exchange and dry matter accumulation were even observed. The possible relationships between growth rate and functioning of photosynthetic apparatus are discussed.

The relations between drought susceptibility index based on grain yield (DSIGY) and key physiological seedling traits in maize and triticale genotypes

The physiological reasons for the differences in sensitivity of C3 and C4 plant species to environmental stresses have not been thoroughly explained. In this study the effects of drought stress on the growth and selected physiological traits were examined in the seedlings of 13 single cross maize (C4 plant) hybrids and 11 spring triticale (C3 plant) breeding lines and varieties differing in drought sensitivity. For plants in the seedling stage the results demonstrated a genetic variation in dry matter accumulation of shoots and roots (DWS, DWR), number (N) and length (L) of particular components (seminal, seminal adventitious, nodal) of the root system, membrane injury by soil drought (LID), osmotic and high temperature stress (LIOS, LIHT), water potential (ψ), water loss (WL), grain germination in osmotic stress (FG, PI), and seedling survival (SS). Seedlings grown under moderate soil drought showed a decrease in dry matter of the top parts and roots and a decrease in the length of seminal, seminal adventitious and nodal roots in comparison to seedlings grown in control conditions. The observed harmful effects of drought stress were more distinct in drought sensitive genotypes. Used in this paper drought susceptibility indexes (DSIGY) were calculated in other experiment by determining the changes in grain yield (GY) under two soil moisture levels (irrigated and drought). The variation of DSIGY for maize ranges from 0.381 to 0.650 and for triticale from 0.354 to 0.578. The correlations between DSIGY and laboratory tests (LI, FG, SS) confirmed that they are good indicators of drought tolerance in plants. The highest values of genetic variation were observed in LI, DWS, SS and WL and the lowest in the measurements of ψ FG, PI, LS, LSA and LN. The correlation coefficients between LIOS and LIHT tests were, in most of the considered cases, statistically significant, which indicates that in maize and triticale the mechanisms of membrane injury caused by simulated drought or high temperature are physiologically similar. It can be concluded that an approach to the breeding of maize and triticale for drought tolerance using these tests can be implemented on the basis of separate selection for each trait or for all of them simultaneously. In that case, it would be necessary to determine the importance of the trait in relation to growth phase, drought timing and level, as well as its associations with morphological traits contributing to drought tolerance. The obtained values of the correlation coefficient between laboratory tests suggest that the same physiological traits may be applied as selection criteria in drought tolerance of maize and triticale genotypes.

Erratum to: The relationship between seedling growth and grain yield under drought conditions in maize and triticale genotypes

The effects of drought stress on seedlings’ growth and grain yield of 13 single cross maize hybrids and 11 breeding lines and cultivars of spring triticale were studied in greenhouse and field experiments. In the field experiment, the drought susceptibility index (DSIGY) was calculated by determining the change in grain yield (GY) in conditions with two soil moisture levels (IR, irrigated; D, drought). In the greenhouse experiment the response to soil drought was evaluated using DSIDW, by determining changes in the dry weight (DW) of vegetative plant parts. Marked variations in GY and DW were observed among the studied genotypes. In control conditions, the GY and DW in drought-sensitive genotypes were higher compared to the drought-resistant ones; but in drought conditions, the decreases in GY and DW in resistant genotypes were smaller than in drought-sensitive ones. DSIGY and DSIDW revealed variations in the degree of drought tolerance among the examined maize and triticale genotypes. The values of DSIGY in the field experiment and DSIDW in the greenhouse experiment enabled a division of the studied genotypes into drought-resistant or -sensitive groups. A close correlation between DSIGY and DSIDW was found. The positive linear correlation and determination coefficients between DSIGY and DSIDW were statistically significant (P = 0.05), being equal to R2 = 0.614 (maize) and R2 = 0.535 (triticale). The ranking of the studied genotypes based on DSIGY was in most cases consistent with the ranking based on DSIDW, which indicates that genetically conditioned drought tolerance is similar for plants in the seedling and reproductive growth stages or may at least partly have a common genetic background.

Current insights into hormonal regulation of microspore embryogenesis

Plant growth regulator (PGR) crosstalk and interaction with the plant’s genotype and environmental factors play a crucial role in microspore embryogenesis (ME), controlling microspore-derived embryo differentiation and development as well as haploid/doubled haploid plant regeneration. The complexity of the PGR network which could exist at the level of biosynthesis, distribution, gene expression or signaling pathways, renders the creation of an integrated model of ME-control crosstalk impossible at present. However, the analysis of the published data together with the results received recently with the use of modern analytical techniques brings new insights into hormonal regulation of this process. This review presents a short historical overview of the most important milestones in the recognition of hormonal requirements for effective ME in the most important crop plant species and complements it with new concepts that evolved over the last decade of ME studies.