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Two-week-old pea (Pisum sativum var. Arkal) plants were subjected to elevated temperature (38 ∞C/42 ∞C) in dark for 14Ð15 h. The effect of heat treatment on light-induced phosphorylation of LHCII and LHCII migration in the thylakoid membranes were investigated. The heat treatment did cause a substantial (more than two fold) increase in the extent of LHCII phosphorylation as compared to the control. Upon separation of appressed and nonappressed thylakoid fractions by digitonin treatment, the heat-treated samples showed a decrease in LHCII-related polypeptides from the grana stack (appressed region) over the control. Further, a small increase in the intensity of these (LHCII-related) bands was detected in stromal thylakoid fraction (non-appressed membranes). This suggests an enhanced extent of migration of phosphorylated LHCII from appressed to non-appressed regions due to in vivo heat treatment of pea plants. We also isolated the LHCII from control and heat treated (42 ∞C) pea seedlings. Analysis of CD spectra revealed a 5Ð6 nm blue shift in the 638 nm negative peak in heat treated samples suggesting alteration in the organization of Chl b in the LHCII macro-aggregates. These results suggest that in vivo heat stress not only alters the extent of migration of LHCII to stromal region, but also affects the light harvesting mechanism by LHCII associated with the grana region.

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The concentration of proline in shoots of rice (Oryza sativa) seedlings raised in distilled water was about 3.3 times higher than in the seedlings raised in modified B5 medium. The shoots of seedlings raised in B 5 medium which was depleted of calcium, iron, magnesium or potassium had a higher concentration of proline than those grown in standard B 5 medium. The shoots of seedlings raised in distilled water with iron had a lower level of proline than those in distilled water. These results suggest that iron deficiency leads to high proline accumulation.The electron transport activity of mitochondria from shoots of etiolated seedlings raised in distilled water or iron-depleted B5 medium was significantly lower than those from equivalent seedlings raised with an iron source. As suppression in mitochondrial electron transport leads to an increase in NADH/NAD ÷ ratio, we propose that the prime cause of the proline accumulation during iron deficiency is to readily maintain NADH/NAD ÷ ratio.

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