Reactions of Egyptian landraces of Hordeum vulgare and Sorghum bicolor to drought stress, evaluated by the OJIP fluorescence transient analysis

Landraces of barley and of Sorghum bicolor from Egypt were evaluated for their tolerance to drought stress (DS) using the OJIP test of the chl fluorescence fast induction curve. Water was withheld from 4-week-old, pot-grown plants for 8-10 days, until the volumetric soil water content decreased from 30 to below 5 vol% and the leaves reached relative water contents of <60 %. The plants were rewatered and recovery measurements were taken 24 h later. Comparative studies of the most sensitive and the most tolerant lines of both cereals, as evaluated by their Performance Indices (PIabs), revealed a similar behavior in the sensitive lines, i.e., inhibiting effects of DS on PS II connectivity (occurrence of an L band), oxygen evolving complex (occurrence of a K band) and on the J step of the induction curves, associated with an inhibition of electron transport from Q(A) to Q(B). These effects persisted or were even enhanced in the rewatered plants, which resulted in similar deviations of spider plots of the OJIP parameters in the sensitive lines of both species. In the most tolerant barley accession, drought effects on early'' events (i.e., L, K bands) were much smaller or negligible, and there was no pronounced effect on the J step. However, distinct increases of the I step occurred, pointing to inhibited electron flow to the intersystem electron carriers and beyond PS I. The most tolerant Sorghum line, in contrast, revealed nearly no effects of the DS and recovery treatment on the fluorescence induction curves and OJIP parameters.