During a 5-20 d growth at moderate salinity (7 dS m‘i) in rice seedlings of salt sensitive cultivars Ratna and Jaya a larger decrease in chlorophyll (Chl) a and b contents was observed than in tolerant cvs. CSR-1 and CSR-3. At higher salinity (14 dS m'i) about 40 % declines in both whole chain electron transport and photosystem (PS) 2 activities were observed in the tolerant cvs. and about 62 to 67 % declines in the sensitive ones. No apparent change in PSI activity was observed due to salinization in the both sets of cultivars. Higher rate of Hill reaction was observed in chloroplasts ffom salt stressed seedlings of tolerant cultivars whereas inhibition in this activity was found in the sensitive ones. Chloroplasts isolated from stressed seedlings of sensitive cultivars showed about 31 % reduction in fluorescence emission at 685 nm as well as a major decrease in absorption with shifts in peaks in the visible region of spectrum. Thus salt sensitivity in rice is associated with decreased contents of Chls and carotenoids, PS2 and Hill reaction activities, and fluorescence emission.
Seedlings of Erythrina variegata Lam. exposed to flooding for 10 d showed significant reduction in height, growth rates (leaf area in plant, leaf area index, relative growth rate, and specific leaf mass), biomass, chlorophyli (Chl) and carotenoid contents, and thylakoid membrane organization. Application of triacontanol partially compensated these effects and promoted height, biomass and Chl content. Starch and sugar contents were significantly higher in leaves of flooded seedlings.
Effect of three Zn2+ concentrations, i.e. 0.075 (cl), 7.50 (c2) and 37.5 (c3) jiM, on rice seedlings was studied at three stages, i.e. 1, 14 and 21 d after transplantation. Typical deficiency symptoms were observed in both solution and sand cultures of cl and c2, but the effects were more pronounced in the solution culture. The c3 concentration was toxic. There was marked reduction in growth, chlorophyll (Chl) contents (particularly Chl b), Hill reaction activity, photophosphorylation rate (particularly non-cyclic photophosphorylation), thylakoid phosphorylation, and i'‘C02-fixation at the cl concentration. However, a similar reduction was also observed in thylakoid phosphorylation at the c3 concentration. Hence the optimum zinc concentration in the nutrient medium lied between c2 and c3 Zn2+. By regression the theoretical optimum Zn concentration was calculated as 19.20 pM (1.28 mg kg'i) Zn2+. Partitioning of ^'^C-photosynthates indicated reduced allocation to sugar and starch fractions and increased fřee amino acids concentration at the cl concentration and vice-versa at c2 and c3.
The genetic variation in low temperature sensitivity of eight tomato genotypes grown at suboptimal temperature (19 °C) and at low irradiance (140 pmol m'2 s**) was assessed at the plant, chloroplast and thylakoid membrane levels. Temperature effects on the thylakoid membrane were determined by measuring the maximum fluorescence (Fp) and the maximal fluorescence rise (ADP) of induction traces of leaf discs at decreasing temperatures (30, 28, ... 0 °C). Two discontinuities were found in Fp versus temperature curves: a low temperature break at ca. 12 °C (LTB) and a high temperature break at ca. 22 °C (FITB). Below LTB, sFp and sDP were determined as the temperature induced changes in Fp, respectively ADP. Chloroplast functioning was determined by measuring net CO2 fixation rate (E^) of leaves. Plant performance was determined by measuring the increase in leaf area and sho ot dry mass in time. Correlations between the various parameters were analysed across the genotypic variation found. Chlorophyll (Chl) fluorescence parameters were not correlated with plant performance at suboptimal growth conditions. of leaves was correlated with plant performance, but only at ambient CO2. Effects of stomatal resistance on were large. The Chl fluorescence parameters LTB, sFp and sDP could distinguish between tomato genotypes. Nevertheless, the ranking of the genotypes depended on the specific parameter selected, indicating that each parameter assessed a different aspect of the heterogeneous temperature dependence of Chl fluorescence induction. Their genetic variation suggested that the genotypes differed in the organisation and fimctioning of the thylakoid membrane. These differences were not reflected in of leaves or plant performance.
The influence of a cytokinin, 6-benzylaminopurine (BAP), on chloroplast structure was studied using biochemical methods and electron microscopy. The average degree of thylakoid stacking was determined by digitonin fractionation and differential centrifugation of chloroplasts from tobacco plantlets after treatment with different concentrations of BAP in agar medium during cultivation in viíro. An elevated concentration of BAP in the medium induced an increase in grana stacking. This was in accordance with the lowering of the chlorophyll a/b ratio in these chloroplasts. The relative amoímt of proteins and carotenoids increased in both stromal and (to a lesser extent) granal chloroplast thylakoid fractions with the BAP concentration. The electron microscopic studies revealed nearly the same volume density of thylakoid membranes within chloroplasts of BAP treated plantlets and control ones. In the BAP treated plantlets the chloroplasts were smaller and had a profound accumulation of starch inclusions and a more flattened shape than the chloroplasts of control plantlets. The volume density of plastoglobuli in chloroplasts did not decrease under the influence of BAP,