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Some effects of low, non-freezing temperatures on plants Gallopin, Isabel Gomez


Low, non-freezing temperatures can cause both, harmful and beneficial effects on plants, and this research was carried out to survey some effects on starch and pigment accumulation. Four species were selected on the basis of photosynthetic biochemistry and major systematic grouping. Zea and Gomphrena possess the C₄-dicarboxylic acid pathway typical of certain families of tropical origin, while Triticum and Phaseolus contain the Calvin cycle alone which is typical of plants originating in temperate regions. Zea and Triticum are Monocotyledoneae while Gomphrena and Phaseolus are members of the Dicotyledoneae. Plants of each species were subjected to 10 days of cold treatment starting when they were 10, 21 or 35 days old (15, 26 and 40 days old for Gomphrena), and spectrophotometry measurements of starch, chlorophylls a and b, and carotenoids were carried out during the treatments. The effects of cold temperature depended on species, age, and duration of treatment. All of the species exhibited a significantly higher level of starch in the cold temperature for at least two of the three ages tested. The most dramatic effect of low temperature occurred in Gomphrena when the starch concentration increased to over 2000 per cent of the concentration attained at the warm temperature. Variations in the effect of cold treatment between the different ages tested were more pronounced in the monocots used than in the dicot species studied and variations due to the duration of cold treatment were observed in Gomphrena and Triticum. Cold treatment also caused significant reduction in total chlorophylls, chlorophyll a and chlorophyll b in all the species except Triticum. In Zea, the response to cold decreased as the plants aged, and the duration of cold treatment had a significant effect in Zea and Gomphrena. When the youngest plants only are considered, the response of starch and chlorophyll levels to cold treatment was well correlated with the typical photosynthetic pathway of the species tested. Low temperature had no significant effect on total carotenoid concentration .The effect of low temperature on light transmission by young Zea leaves during the first 48 hours of greening was also examined. Chlorophyll a concentration and leaf light transmission were highly correlated and the more convenient transmission measurements can therefore be used to predict leaf chlorophyll concentration. At the warm temperature used, there was a linear increase in chlorophyll concentration after a 2 hour lag period. Preceding cold treatment caused a longer lag period before chlorophyll began to accumulate at the warm temperature. Also, no chlorophyll accumulated, or there was net chlorophyll breakdown at low temperature. Kinetin treatment did not prevent the decrease in chlorophyll concentration at the low temperature.

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