Effects of changes in growth temperature on photosynthesis and carotenoid composition in Zea mays leaves

The effects of changes in growth temperature on photosynthesis and carotenoid composition were examined in Zen mays L. leaves of different age and different developmental history. The plants were first grown at sub-optimal temperature (14 degrees C) until the full development of the third leaf. At that time, the mature third leaf and the imma ture fourth leaf had a low chlorophyll (Chl) content, a low Chl a/b ratio, a high carotenoid/Chl a+b ratio, a high xanthophyll/beta-carotene ratio, and about 80% of the xanthophyll cycle pool (violaxanthin [V] + antheraxanthin [A] + zeaxanthin [Z]) was in the form of zeaxanthin and antheraxanthin. When the temperature was increased from 14 degrees C to 24 degrees C for three days, increased Chi synthesis, accompanied by an increase in the Chi a/b ratio, took place. The ratios of lutein, neoxanthin, and V+A+Z to Chi a+b decreased markedly whereas no significant changes appeared in the beta-carotene/Chl a+b ratio. Furthermore, there was a sharp decrease in the xanthophyll/beta-carotene ratio and most of zeaxanthin was converted to violaxanthin in the xanthophyll cycle. The third leaf and the tip segment of the fourth leaf, both expanded at 14 degrees C, showed little difference in their pigment contents. However, the rate of CO2 assimilation of the tip segment of the fourth leaf was nearly twice that of the third leaf oil the third day at 24 degrees C, while the photosynthetic activity was similar in both leaves before the transfer to 24 degrees C. During the warm period at 24 degrees C. new leaf tissue (basal segment of the fourth leaf and part of a fifth leaf) was formed. On the third day al 24 degrees C, the pigment content of 24 degrees C-grown leaf tissue did not differ much from that of 14 degrees C-grown leaf tissue with the exception that the total carotenoid content was lower in the former as compared to the latter, mainly because of a lower V+A+Z content. The rate of CO2 assimilation of 24 degrees C-grown leaf tissue was comparable to that of the tip segment of the fourth leaf Regardless of which leaf tissue is considered, reducing the temperature from 24 degrees C to 14 degrees C for 5 days slightly affected the pigment content, but violaxanthin was largely converted to zeaxanthin and antheraxanthin in the xanthophyll cycle. The results indicate that compared to old leaf tissue of mature leaves, physiologically younger leaf tissue of immature leaves is much more able to recover from depressions in the photosynthetic activity induced by growth at sub-optimal temperature when the plants experience optimal growth temperatures. but that factors other than the pigment content must determine this capability.