Chilling-induced changes to carotenoid composition, photosynthesis and the maximum quantum yield of photosystem II photochemistry in two maize genotypes differing in tolerance to low temperature

The changes to the carotenoid composition and photosynthetic activity induced by chilling in the light were examined under controlled environment in the third leaf of a chilling-tolerant genotype (Z7) and a chilling-sensitive genotype (Penjalinan) of Zea mays L. In control plants, grown at 24/22 degrees C (day/night) under a photon flux density of 500 mu mol.m(-2).s(-1) and a photoperiod of 12 h, the rate of CO2 assimilation and the carotenoid composition did not differ significantly in the two genotypes. However, the chilling-tolerant genotype was able to maintain a higher photosynthetic capacity than the chilling-sensitive genotype when the plants were chilled far 5 days at 10/8 degrees C (day/night). The stress led to a reduction in the maximum quantum efficiency of photosystem II (PSII) photochemistry, as judged by the decrease in the ratio of variable to maximum chlorophyll a fluorescence (F-v/F-m), but no significant differences appeared between the two genotypes. The maximum quantum efficiency of PSII photochemistry recovered hater from chilling than the rate of CO2 assimilation on transfer of the chilled plants to 24 degrees C for 5 days. The race of recovery was similar in the two genotypes. During the stress, there was a decrease in the chlorophyll a content which was accompanied by a decrease in the beta-carotene content and an increase in the content of the carotenoids of the xanthophyll cycle. Opposite reactions occurred during recovery. The contents of lurein and neoxanthin were hardly affected by the temperature changes. The mast important impact of chilling was a large and reversible de-epoxidation of violaxanthin to zeaxanthin in the xanthophyll cycle which was more pronounced in the chilling-sensitive genotype than in the chilling-tolerant genotype. Short-term (minutes to hours) exposure of plants or leaf segments to various temperature and light stress conditions revealed that the temperature-and light-dependent changes in the maximum quantum efficiency of PSII photochemistry and the degree of violaxanthin de-epoxidation were generally similar for the two genotypes. The results indicate that it is unlikely that the content and composition of carotenoids and the operation of the xanthophyll cycle are major factors in determining the better ability of chilling-tolerant genotypes, as compared to chilling-sensitive ones, to cope with low temperature-induced reductions in photosynthesis.