Changes in the pool of soluble sugars induced by dehydration at the heterotrophic phase of growth of wheat seedlings.

Loss of dehydration tolerance coincides with a shift from heterotrophy to autotrophy during post-germination growth of spring wheat seedlings. This critical stage falls on the fifth day following imbibition. Till the sixth day of experiment light had no effect on dry weight of the seedlings but the survival of six day old seedlings was reduced by half upon dehydration. Germinating seeds in the presence of 5 mM glucose, fructose, mannose or sucrose did not promote seedling growth but either increase (glucose, fructose) or decreased (mannose, sucrose) the survival of dehydrated seedlings. Protection against dehydration by the former sugars was correlated, irrespective of the seedling age, with the decrease of sugar pool in seeds and increase in shoots (coleoptile and first leaf) and roots. The opposite changes were provoked by the sugars hampering seedling survival. Generally, survival of wheat seedlings was not correlated with the size of soluble sugar pool but its distribution and composition. Lower mobilisation of soluble sugars in seed, lower proportion of reduced sugars to sucrose and higher share of raffinose is characteristic for the tolerant four day old seedlings and those grown in the media containing glucose or fructose. The results presented indicate that higher proportion of reduced sugars to sucrose and lower share of raffinose in six day old seedlings seems to be associated with the loss of dehydration tolerance of these seedlings, despite heterotrophic character of growth.

Genotype-dependent proteolytic response of spring wheat to water deficiency.

Changes in proteolytic activities in response to water deficiency have been investigated in ten genotypes of spring wheat (Triticum aestivum L.) differing in response to water deficit stress and ability to acclimate. To determine subcellular localization and the type of proteases, mesophyll protoplasts isolated from wheat leaves were purified. Proteolytic activities were assayed using azocasein in the case of vacuolar proteinases at pH 5.0 and 125I-lysozyme in the case of extravacuolar ATP-dependent proteinases at pH 8.2. ATP-dependent proteolytic activity was found to be confined to the extravacuolar fraction while the azocaseinolytic activity to vacuoles. Dehydration increased vacuolar azocaseinolytic activity at both stages of plant development (shooting and heading), but the increase was significantly lower in more tolerant genotypes. The extravacuolar energy-dependent 125I-lysozyme degradation was low at the shooting stage but it was higher in the genotypes with a greater critical water saturation deficit. At the heading phase in the non-acclimated flag leaves ATP-dependent 125I-lysozyme degradation decreased in a genotype-dependent manner, but was enhanced upon acclimation to the same extent irrespective to the genotype ability to acquire dehydration tolerance during acclimation. The results presented indicate that both pathways of protein degradation are interlinked upon dehydration and are genotype dependent.

Endoproteinase activities in wheat leaves upon water deficit.

In wheat leaves acclimated and non-acclimated to water deficit the azocaseinolytic activities of endoproteinases were increased about 7-fold under drought conditions. Under such conditions both the pH dependence profile and the endoproteinase pattern were also changed. The predominant contribution of serine proteinase (about 50% of total endoproteinase activity) remains unaltered in the drought stressed leaves. Cysteine proteinase was induced to the same extent in the drought-stressed leaves irrespective of the acclimation pretreatment, while the contribution of aspartic proteinase was reduced upon water deficit but in the acclimated stressed leaves was as high as in the non-stressed leaves. These changes in the pattern of endoproteinases seem to imply that the water deficiency affects endogenous proteolysis.

Energy metabolism in plants under water deficits.

Regardless of the mechanisms of stress resistance, the maintenance of functional integrity in plants imposes an energetic cost. This mini-review summarized the present knowledge on energy metabolism in plants under drought conditions with the focus on studies performed on wheat in author's laboratory.

Induction of microsomal drug metabolizing enzymes by phenobarbitone in the rats exposed to increased environmental temperature.

Exposure of rats for 3 consecutive days (6 h a day) to 28 degrees C or 35 degrees C does not lead to changes in the induction of hepatic microsomal cytochrome P-450 associated monooxygenases by phenobarbitone as compared with control animals exposed to 21 degrees C. These results suggest that environmental temperature does not change the capacity of phenobarbitone to induce drug metabolizing enzymes in rat liver.

Effects of benzodiazepines on enzymes metabolizing drugs. IV. Effect of diazepam and oxazepam on hepatic microsomal drug metabolizing enzymes in rats exposed to high environmental temperature.

Administration of diazepam or oxazepam caused a different response of the rat hepatic microsomal cytochrome P-450 dependent monooxygenase system. Both drugs produced significant decrease in the activity of NADH: cytochrome c oxidoreductase in rats exposed to 21 degrees C, but not to 28 degrees C and 35 degrees C, and did not change the activity of aniline hydroxylase, aminopyrine N-demethylase and 4-nitroanisole O-demethylase and cytochrome b5 level at any tested temperatures. Oxazepam, but not diazepam, caused a decrease in cytochrome P-450 content in rats exposed to 21 degrees C only. The results indicate that the high ambient temperature modifies the effect of tested benzodiazepines on the activity of some microsomal enzymes.

NAD kinase activity in wheat leaves under water deficit.

Total NAD kinase activity remained unaltered in the drought non-adapted wheat leaves under water deficit, but gradually decreased with water deficit in the adapted ones. The share of the calmodulin-dependent enzyme was significantly higher in the drought-hardened than in non-hardened plants; however, under severe water deficit the activity of the enzyme dropped by half. It seems, therefore, that NAD kinase activity does not limit phosphorylation of NAD in dehydrated plant tissues.

Influence of Water Stress upon Photosynthetic Carbon Metabolism in Wheat.

Two kinds of effects of water stress on flag leaves of spring wheat (Triticum aestivum L. cv. Kolibri) were recognized: the direct effect, when drought affected the expanded blade of the flag leaf and the indirect one, when drought pretreatment affected the leaf blade during tissue differentiation. As a direct effect of water stress on the leaf, a decreased amount of (14)C incorporated into all analyzed photosynthates was observed. Differences in (14)C distribution among the studied photosynthates indicated that water stress decreased the carbon flow from intermediates to end products of the photosynthetic metabolism. Drought pretreatment protected (to some extent) the carbon photosynthetic metabolism against the inhibitory effect of the subsequent water stress. The modifications of photosynthetic carbon metabolism observed seem to be involved in adaptation of plants to the water stress conditions.