Pieter J. C. Kuiper

Effects of internal and external cytokinin concentrations on root growth and shoot to root ratio of Plantago major ssp pleiosperma at different nutrient conditions.

In Plantago major L. an enormous genetic variability is present for a large number of plant traits (Van Dijk and Van Delden, 1981; Kuiper, 1982, 1983; Kuiper and Smid, 1985). Differences in relative growth rates (RGR) for shoot and roots were observed among inbred lines of P. major. Inbred lines also differed largely in the rate of growth responses, when plants were transferred from a nutrient-rich growth solution (100%) to a 50 times diluted nutrient solution (2%) and vice versa. Quick growth responses in plants of an inbred line belonging to subspecies pleiosperma (Pilger) transferred from a 100% to a 2% solution (100–2% plants) were accompanied by a rapid decrease in shoot to root ratio (S/R). The rapidity of the responses in P. major ssp pleiosperma and preliminary determinations of the contents of several ions raised the question about the decisive role of the availability of minerals in growth regulation.

Responses to Iron-Deficiency in Arabidopsis-Thaliana - The Turbo Iron Reductase does not depend on the Formation of Root Hairs and Transfer Cells.

Arabidopsis thaliana (L.) Heynh. Columbia wild type and a root hair-less mutant RM57 were grown on iron-containing and iron-deficient nutrient solutions. In both genotypes, ferric chelate reductase (FCR) of intact roots was induced upon iron deficiency and followed a Michaelis-Menten kinetic with a Km of 45 and 54 μM FeIII-EDTA and a Vmax of 42 and 33 nmol Fe2+·(g FW)−1·min−1 for the wild type and the mutant, respectively. The pH optimum for the reaction was around pH 5.5. The approximately four fold stimulation of FCR activity was independent of formation of root hairs and/or transfer cells induced by iron deficiency. Iron-deficiency-induced chlorosis and the development of a rigid root habit disappeared when ferric chelate was applied to the leaves, while FCR activity remained unchanged. The time course of the responses to iron deficiency showed that morphological and physiological responses were controlled separately.

Actual cytokinin concentrations in plant tissue as an indicator for salt resistance in cereals

Growth rates of roots and shoots of hydroponically grown plants of a salt resistant variety of barley decreased rapidly after an exposure to 65 M m-3 sodium chloride. This growth rate reduction tended to be temporarily and it was accompanied by a lowered shoot to root ratio. At the same time growth reduction took place, the cytokinin concentrations in root and shoot tissue decreased rapidly too, as they were measured by an enzyme-linked immuno assay. The addition of 5·10-9M m-3 benzyladenine (BA) retarded the decreases of growth rates, shoot to root ratio and internal cytokinin concentrations.Growth rates of roots and shoot of identically grown plants of salt sensitive varieties of barley maintained their growth rates and shoot to root ratio after an exposure to NaCl for at least ten days in combination with unchanged levels of endogenous cytokinins. After ca 14 days NaCl induced severe decreases in RGR values, but not in shoot to root ratio. Addition of benzyladenine inhibited growth to some extent and enhanced the cytokinin concentration.It was concluded, that cytokinin concentrations measured directly after exposure to NaCl form a promising screening method for salt resistance. The addition of BA made salt resistance varieties behave as salt sensitive varieties.

Effect of N fertilizer top-dressing at various reproductive stages on growth, N2 fixation and yield of three soybean (Glycine max (L.) Merr.) genotypes

Soybean (Glycine max (L.) Merr.) is one of the most important food and cash crops in China and a key protein source for the farmers in northern China. Previous experiments in both the field and greenhouse have shown that N2 fixation alone cannot meet the N requirement for maximizing soybean yield, and that N top-dressing at the flowering stage was more efficient than N top-dressing at the vegetative stages. However, the effect of N fertilizer application at other reproductive stages of soybean is unknown. Thus, a field experiment was conducted to study the effects of N applications at various reproductive stages on growth, N2 fixation and yield of three soybean genotypes. The results showed that starter N at 25 kg ha−1 resulted in minimum yield, total N accumulation and total amount of N2 fixed in all three genotypes. N top-dressing at 50 kg ha−1 at either the V2 or R1 stages, significantly increased N accumulation, yield and total amount of N2 fixed in all three genotypes. However, N top-dressing at the same rate at either the R3 or R5 stage did not show this positive effect in any of the three genotypes. Thus, the best timing for N top-dressing during reproduction is at the flowering stage, which increased seed yield by 21% for Wuyin 9, 27% for You 91-19, and 26% for Jufeng, respectively, compared to the treatment without N top-dressing.

RELATION BETWEEN RELATIVE GROWTH-RATE, ENDOGENOUS GIBBERELLINS, AND THE RESPONSE TO APPLIED GIBBERELLIC-ACID FOR PLANTAGO-MAJOR

Relationships between relative growth rate (RGR), endogenous gibberellin (GA) concentration and the response to application of gibberellic acid (GA(3) ) were studied for two inbred lines of Plantago major L., which differed in RGR. A4, the fast-growing inbred line, had a higher free GA concentration than the slow-growing W9, as analyzed by enzyme immunoassay. GA(3) application increased total plant weight and RGR(3) particularly for the slow-growing line. Chlorophyll a content and photosynthetic activity per unit leaf area were decreased, while transpiration rate was unaffected by GA(3) application. The increase in RGR by GA(3) application was associated with an increased leaf weight ratio; specific leaf area and percentage of dry matter in the leaves were only temporarily affected. Root respiration rate per unit dry weight was unaffected. The correlation between low RGR, low GA concentration and high responsiveness to applied GA(3) supports the contention that gibberellins are involved in the regulation of RGR. However, the transient influence of GA(3) application on some growth components suggests the involvement of other regulatory factors in addition to GA.

Root functioning under stress conditions: An introduction

The only difference from the usual approach in plant sciences is that the experimental plants are exposed to suboptimal environmental conditions or even severe conditions, the so-called stress conditions.

The Effect of H2S Fumigation on Various Spinach (Spinacia oleracea L.) Cultivars Relation between growth inhibition and accumulation of sulphur compounds in the plant

Summary Several cultivars of spinach ( Spinacia oleracea L.) were continuously fumigated with 0.3 8 mg m −3 H 2 S. For the two cultivars tested, Subito and Dynamo, the rate of germination was not affected by H 2 S fumigation, but the total percentage of germinated seeds was slightly increased. Shoot growth of all ten cultivars tested, with the exception of cv. Monosa, was inhibited by 50 % on the average by H 2 S. Monosa was significantly less reduced than the other cultivars tested at a day and night temperature of 16/12 °C and more reduced at 18/18 °C. H 2 S reduced the growth in length of the cotyledon. This reduction was positively correlated with the reduction in growth of the total shoot. Dry matter content was slightly increased in the plants exposed to H 2 S. Water-soluble non-protein sulphydryl and sulphate content increased to various extents in both cotyledons and leaves. There was no direct relation between accumulation of sulphur compounds and reduction of growth.

Mineral Nutrition: Sources of Nutrients for Land Plants from Outside the Pedosphere

From the beginning of the colonization of the land surface by plants, rain must have been a source of nutrients. There are global cycles in both the water and salts of the oceans; it takes a period of about 80 million years to transport the ocean salt, by means of sprays and aerosols, over the edges of the continents (HOLMES 1937) and 5000 years to transport the ocean water. In addition to the ocean, chemical transformations of nitrogen in the atmosphere and geological upheavals such as volcanoes can provide a wide variety of plant nutrients in gaseous, dissolved, and particulate forms. The rates at which these nutrients are deposited on the land surface are highly variable and depend on climate and prevailing wind direction. At most, however, they can support only very slow rates of plant growth. Plant communities, such as raised Sphagnum bogs, which are almost totally dependent on the atmosphere for their nutrients, have intrinsically low rates of biomass production (PEARSALL and GOREHAM 1956; PAKARINEN 1978).

Combined electron-spin-resonance, X-ray-diffraction studies on phospholipid vesicles obtained from cold-hardened wheats

Phospholipid multibilayers, obtained from two cultivars of thermally acclimated wheats of different frost resistances (Triticum aestivum L. cv. Penjamo 62, the sensitive cultivar, and T. aestivum L. cv. Miranovskaja 808, the frost-resistant cultivar), were investigated using electron-spin-resonance and X-ray-diffraction techniques. The former technique revealed two breaks in the motion of the spin-labelled fatty acid 2-(14-carboxyte-tradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxyl, for both cultivars (+3°C,-17° C and +5° C,-18° C, respectively) when grown at 22° C. The resistant cultivar compensated for exposure to cold (+2° C) by shifting the onset of the apparent phase-separation temperature from +3° C to-16° C. The sensitive cultivar was unable to do so. X-ray diffraction did not reveal fluid-to-gel transitions between +20° C and-10° C in any of the samples. The possible role of the formation of relatively ordered aggregates or clusters of lipid molecules discerned by spin probe within the otherwise freely dispersed liquid-like lipids is discussed in terms of freezing injury of plants.

Role of Nitrate in Growth of Higher Plants with Emphasis on Regulation of Nitrate Accumulation

Growth of higher plants is strongly dependent on mineral nutrition and changes therein. Experiments carried out in our laboratory in which the level of macronutrients in the solution was changed, both from high to low and from low to high concentrations, showed that nitrate probably is the most important component of the nutrient solution as to causing the observed positive and negative effects on growth (Lambers et al. 1981; Stulen et al. 1981). In Plantago the negative effect of a switch from high to low nutrient conditions on shoot growth was immediate; shoot growth did not decrease as a result of shortage of mineral nutrients. Apparently shoot growth was regulated in a manner which did not involve actual concentrations of minerals in the plant tissue itself, for growth stopped before any decrease in nitrate concentration in the tissue was observed (Lambers et al. 1981; Stulen et al. 1981).