Role of light in changes in free amino acid and polyamine contents at chilling temperature in maize (Zea mays)

The effect of irradiance on changes in photosynthesis, free amino acids and polyamines was investigated. Two-week-old maize (2ea mays L.) plants were chilled at 5 degrees C in the light (250 mu mol m(-2) s(-1) PAR) or dark. The chlorophyll fluorescence ratio, F-v/F-m, decreased in the light by ca 50% but did not change in the dark, Similarly to the F-v/F-m, there was no change in the transpiration rate or the stomatal conductance in the dark, while these parameters decreased by ca 55% in the light. The net photosynthesis rate declined in both cases, but to a far greater extent in the light (73%) than in the dark (40%). The intercellular CO2 partial pressure increased by ca 50% in all cases. The foe amino acid contents increased compared to the control during the cold treatment. In most cases this increase was more pronounced in the light than in the dark. There was a continuous increase in the putrescine level, which was more pronounced in the light than in the dark. The spermidine content increased one and a half times after one day in the light but decreased by 70% in the dark compared to the control values. From the second day a 50% decline in the spermidine content was observed in the light and an 80% decline in the dark. These results suggest that light has an influence not only on the photosynthetic processes during chilling stress but also on other stress markers such as polyamines and free amino acids.