| Abstrakt: |
The effects of sub-optimal day/night temperatures (15°/10°C; PPFD 250 µmol m-1 s-1), or low light intensity (25°/18°C; PPFD 100 µmol m-2 S-1), or sub-optimal temperatures combined with low light intensity (15/10°C; PPFD 100 µmol m-2 s-1) on hypocotyl and leaf growth were studied in watermelon (Citrullus lanatus) seedlings. We also measured the activities of anti-oxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as tissue concentrations of malondialdehyde (MDA), proline, and soluble sugars under the three experimental conditions and in an optimal-conditions control group. Our observations indicated that hypocotyl elongation and leaf area expansion were inhibited by sub-optimal temperatures. Stem diameter growth was inhibited by low light intensity, whereas low light had a positive effect on hypocotyl elongation and leaf area growth. However, the growth of hypocotyls and leaves were significantly inhibited by the combination of sub-optimal temperatures and low light intensity. After exposure to sub-optimal temperatures alone, or in combination with a low light intensity, SOD activity increased by 61.9% and 39.5%, and POD activity increased by 185.1% and 120.7%, respectively. However, CAT activity declined by 22.0% under sub-optimal temperatures conditions. Moreover, the low light intensity increased CAT activity by 38.1%, but had weak effect on both SOD and POD activities. The activities of SOD and POD probably increased as a result of the activation of the cellular anti-oxidant defence system. CAT activity appeared to be more strongly affected by sub-optimal temperatures or low light intensity compared with the combined effect of low temperatures and low light. Sub-optimal temperatures increased MDA concentrations and caused lipid peroxidation in cell membranes. However, low light could alleviate the damage due to lipid peroxidation under sub-optimal temperatures. Proline and soluble sugar concentrations increased significantly when exposed to sub-optimal temperatures alone or in combination with low light intensity. The accumulation of proline and soluble sugars demonstrated the positive effects of both stresses on osmotic adjustment and metabolic regulation. These findings indicated that watermelon seedlings differed in their growth and physiological responses to sub-optimal temperatures and/or low light intensity, and that sub-optimal temperatures can activate the anti-oxidant system in leaves, the latter being related to the increase in ROS scavenging enzyme activities. However, a low light intensity could alleviate the oxidative damage caused to leaves under sub-optimal temperatures. [ABSTRACT FROM AUTHOR] |
