Olga Votrubová

Growth and biomass allocation of sweet flag (Acorus calamus L.) under different nutrient conditions

The antropogenically-induced process of eutrophication is accompanied by changes in the structure and function of the whole wetland ecosystem. Since the shift in a species ability to survive in original habitats is a commonly observed feature, the performance of individual wetland plants under high nutrient load is of a particular interest. Acorus calamus is a common littoral plant species of the European wetlands, which are characteristic by high trophic status. The effect of nutrients (N, P) per se, as a key part of the complex eutrophication process on the growth, biomass allocation, and biometric characteristics of Acorus calamus, is the main aim of the study. The study follows the effects of different levels of phosphorus (0.5 and 1.5 mM) and nitrogen (1.87; 7.5 and 18.5 mM), likewise the effect of NH4+ and NO3− form, on the growth of Acorus. Special attention is dedicated to the growth of underground organs, particularly roots, because of their direct contact with the flooded substrate.While P enrichment (1.5 mM) had no substantial effect on the growth of Acorus, high N treatment (18.5 mM) negatively affected its growth. 50, 30 and 50% reduction in shoot, rhizome, and root biomass accumulation, respectively, was found under high N supply. On the whole, lower number of roots with high proportion of short (30–60 mm long) roots, together with higher proportion of young roots with no developed lateral roots and high proportion of injured roots, particularly those more differentiated with developed lateral roots, characterised root system of Acorus plants growing under high N supply in comparison to the conditions of lower nutrient supply. Some similar features found under high N supply were founded also under pure NH4+ nutrition. Since NH4+-N was the only N-form elevated under high N treatment, we tried to separate the effect of NH4+ only nutrition and the effect of high N load. Possible consequences of intensive NH4+-N nutrition are discussed in connection with differences between the growth reactions of plants under experimental conditions and under eutrophic natural sites where other factors than high N influence growth of the plants.

Aerenchyma formation in maize roots

Maize (Zea mays L.) is generally considered to be a plant with aerenchyma formation inducible by environmental conditions. In our study, young maize plants, cultivated in various ways in order to minimise the stressing effect of hypoxia, flooding, mechanical impedance or nutrient starvation, were examined for the presence of aerenchyma in their primary roots. The area of aerenchyma in the root cortex was correlated with the root length. Although 12 different maize accessions were used, no plants without aerenchyma were acquired until an ethylene synthesis inhibitor was employed. Using an ACC-synthase inhibitor, it was confirmed that the aerenchyma formation is ethylene-regulated and dependent on irradiance. The presence of TUNEL-positive nuclei and ultrastructural changes in cortical cells suggest a connection between ethylene-dependent aerenchyma formation and programmed cell death. Position of cells with TUNEL-positive nuclei in relation to aerenchyma-channels was described.

Differences in anatomical structure and lignin content of roots of pedunculate oak and wild cherry-tree plantlets during acclimation

The lignin contents and anatomical structure of roots of wild cherry (Prunus avium L.) and pedunculate oak (Quercus robur L.) plantlets were compared to explain differences in response during transfer from in vitro to ex vitro conditions. Lignification of cell walls increased significantly in both oak and cherry roots during the period of acclimation and finally lignin content of root tissues of in vitro propagated plantlets reached the levels not significantly different from seedlings grown in soil. Later on when secondary tissues appeared, lignified secondary xylem constituted most of the tissues of both species. The most conspicuous interspecific difference in root structure was the presence of phi-thickenings in cortical layers just outer to endodermis in cherry roots cultivated ex vitro. Formation of phi-thickenings was avoided in vitro and their presence thus seems to be under environmental control. Suberised well established exodermis was present in roots of oak but not detected in those of cherry. Very early development of exodermis in oak roots, preceding suberisation of endodermis, was recorded in vitro but not in well aerated soil. While multilayered and well-developed cork occurred in oak, only thin walled and less suberised secondary dermal tissues were found in cherry.

EFFECT OF NITROGEN OVER-SUPPLY ON ROOT STRUCTURE OF COMMON REED

Plants of the common reed (Phragmites australis (Cav. Trin. exSteud.) were treated with high doses of nitrogen in an experiment performed in a sand culture and lasting one vegetation period. Nitrogen treatment resulted in alterations of growth; the increased growth of rhizomes and stalks was connected with production of significantly shorter roots. The differences in root growth were connected with changes in the internal root structure. In rhizome-borne roots, treatment with high nitrogen reduced the formation of aerenchyma and lignified layers in subapical regions. No substantial differences were observed in starch occurrence in the roots under the two treatments.

The Influence of Nitrogen Nutrition on the Carbohydrate and Nitrogen Status of Emergent Macrophyte Acorus calamus L.

Carbon and nitrogen balance in Acorus calamus, a wetland species colonising littoral zones with a high trophic status, was studied under experimental conditions using water or sand culture with a defined composition of the nutrient solution. Influence of graded level of N (1.86, 7.5 and 18.6 mM) and/or forms of N (NH4+ versus NO 3–) on the content of non-structural carbohydrates, free amino acids, total C, and total N was studied in Acorus rhizomes and roots to find possible connection with a reduced growth of Acorus plants under high N and NH4+–N nutrition described in our previous study [Vojtíšková et al., 2004. Hydrobiologia 518: 9–22]. High N availability and pure NH4+–N nutrition affected the C/N balance of rhizome and root systems of Acorus in a similar way. NH4+–N was the only form of N elevated under the high N treatment. The major proportion of the total non-structural carbohydrates (TNC) was starch (91–93% and 51–64% in rhizomes and roots, respectively). The content of starch was significantly and and negatively affected by high N availability (P = 0.001), as well as by NH4+–N nutrition (P=0.001). Amounts of simple soluble carbohydrates (sucrose, glucose, and fructose) were negligible in comparison to starch in rhizomes and branched roots (up to 5% of TNC), while roots without developed lateral roots (unbranched) contained up to 33% of TNC in the form of simple soluble sugars. Moreover, high hexoses/sucrose ratio, low starch/soluble sugars ratio, high content of N, and low C/N ratio support the notion that unbranched roots are metabolically active young roots with tissue differentiation in progress. A high content of free amino acids, typically with dominance of N-rich amino acids (Arg-46%, Gln-8%, Asn-7%), was found simultaneously with a low carbohydrate content under high N supply, which indicates that NH4+ received is effectively incorporated into the organic form by this species. Since the decrease in carbohydrate content was not accompanied by luxurious growth, other possible carbon consuming processes were discussed in relation to NH4+ nutrition. More dramatic changes in total N than C were found under high N availability resulting a shift in C/N ratio in favour of N. Although the shift towards N metabolism was obvious, no serious carbohydrate depletion occurred, which could explain the reduced growth of Acorus plants under high N and sole NH4+–N nutrition described previously.

Non-destructive stereological method for estimating the length of rigid root systems

A non-destructive method of total vertical projections for estimating the length of rigid root systems, not introduced yet in plant sciences, is described. It is demonstrated on measuring less and more dense root systems of seedlings of Zea mays grown at hypoxic or control conditions. Photographs of six vertical projections (30° apart) of each root system were taken and evaluated. The method being based on proved mathematical formula offers unbiased estimation of the length of a rigid root system, curved in three-dimensional space, by non-destructive means. Thus, it is applicable during ongoing experimentation on plants grown in a solution culture. It was shown that less than 120 intersections between the root projection and test lines in one photograph ensured sufficient precision of the method and that the observer subjectivity could be overcome by presented instructions.

Distribution of stomata on the second leaf ofZea mays following root hypoxia

The changes in leaf dimensions, transverse and longitudinal gradients in stomatal density and the total number of stomata under the influence of root hypoxia were followed. In spite of considerably reduced leaf area following hypoxia the total number of stomata per leaf was not changed significantly. The resulting increase in stomatal density was not uniform being the most prominent in the basal part of the leaf where the distances between stomata and between rows of stomata became shorter.

The influence of IAA on the uptake of potassium, calcium, magnesium, water absorption and growth in young maize seedlings

The influence of IAA in two concentrations (10−8M and 10−5M) on relations between growth, water absorption and cation uptake and accumulation was tested.IAA in a higher concentration retarded growth remarkably. First of all, potassium uptake and water absorption were significantly decreased while the uptake of divalent cations was affected later and less remarkably. 10−8 M IAA accelerated the growth rate slightly together with acceleration of water absorption and cation uptake.