Influence of soil drought (40 d) on gas exchange of 10 cultivars of spring cereals (wheat, barley, triticaie and oats) grown in growth chamber was studied. When soil water content was decreased from 60 to 35 % of Ml water capacity, a new steady levels of net photosynthetic rate, transpiration rate and stomatal conductance (about twice, 3-4 and 2-3 fold lower, respectively) were observed after 3 d for both studied oat cultivars and after 5 d for others. These levels were maintained almost the same till the end of the experiment. Calculated water use efficiency (WUE) of water stressed plants increased 3-4 fold, the highest being for barley while the lowest for Oats. At die beginning of the night dark respiration of well watered plants was a little higher than that of water stressed plants but at the end of ihe night was the Sáme independently of water treatment, aithough 20-30 % lower than at the begitming of the night.
A trace amount of chlorophyll (Chl) a was found in addition to protochlorophyllide (PChlide) a and protochlorophylls (PChls) a in acetone extracts of etiolated cucumber cotyledons by HPLC. There was, however, no chlorophyllide (Chlide) a, which was present in extracts from illuminated cotyledons. After 10 min exposure of cotyledons to light, all PChlide a was photoreduced to Chlide a. Hence, the whole pool of PChlide seems to be photoactive. The "photoinactive" spectral form PChl(ide) F633 was identified as a mixture of monovinyl-PChls a esterified by different alcohols.