Effects of low temperature on chlorophyll (Chl) fluorescence, gas exchange rate, the amounts of xanthophyll cycle pigments (Xp) and the activities of several antioxidant enzymes were examined in the 8th leaf of two rice (Oryza sativa L.) cultivars (japonica and indica types) and rbcS antisense rice. All plants were grown hydroponically at 25/20 degrees C (day/night), and then exposed to 20/17 degrees C (day/night) after full expansion of the 8th leaf, or exposed to either 20/17 degrees C or 15/13 degrees C (day/night) during the expansion of the 8th leaf. All plants exposed to low temperatures showed a decrease in CO(2) assimilation rate without photoinhibition, and increases in the fraction of thermal dissipation in PSII, and in the electron flux through the water-water cycle (WWC) were observed. Although the increase of thermal dissipation was associated with increases in the ratio of carotenoids to Chl, the ratio of Xp to carotenoids and the de-epoxidation state of Xp, the increase of the electron flux of WWC was not accompanied by an increase in the activities of antioxidant enzymes. Such photoprotective responses did not differ between during and after full expansion of the leaf, and did not differ among the three genotypes. Quantitative analyses on the dissipation of excess light energy showed that thermal dissipation makes a larger contribution than WWC. Thus, although low temperature led to a decrease in CO(2) assimilation, rice potentially coped with the excess light energy by increasing the thermal dissipation and the electron flux of WWC under low temperature irrespective of leaf development and genotypes.

The effects of temperature on photosynthesis, ribulose-bisphosphate carboxylase (Rubisco) content and whole plant growth were investigated in the assimilation shoots of a rose (Rosa hybrida L.). Assimilation shoots were grown at two different day/night temperature regimes of 20/15°C (LT) and 30/25°C (HT) for 42 days after 1-month growth. Although LT initially suppressed the photosynthetic rate during the first 7 days, prolonged growth at LT enhanced potential photosynthesis. This was associated with increases in Rubisco and N contents at the level of a single leaf. Rubisco content and the photosynthetic rate at 25°C were 2.8-fold and 1.6-fold higher in the LT plants than in the HT plants at day 42, respectively. The relative growth rate at the level of the whole plant was lower in the LT plants during the first 28 days and the leaf area ratio was smaller in the LT plants throughout the experiment. However, enhanced photosynthesis during growth at LT led to increases in the net assimilation rate at the level of the whole plant, and final biomass at day 42 did not differ between the two temperature treatments. To enhance the photosynthetic capacity in assimilation shoots of a rose, cultivation at 20/15°C is better than cultivation at 30/25°C.

We investigated the effects of nitrogen fertilizer levels in nutrient solution applied before/after flower budding on blasting in the winter flowering of Eustoma grandiflorum (Raf.) Shinn. Application of a solution with a high nitrogen concentration after flower budding increased the number of flower buds and fresh weight of cut flower, whereas the rate of flower-bud blasting was increased by application of high concentration nitrogen. The relationship between the rate of flower-bud blasting and the nitrogen concentration in the whole plant showed a linear function. The rate of flower-bud blasting was found to be proportional to the fresh weight of the cut flower. The increased nitrogen levels applied after flower budding induced flower-bud blasting at the upper nodes as well as the lower nodes. As a result, flowering was delayed by blasting. Moreover, the total biomass production increased with the increase in nitrogen levels after flower budding. When the flower bud developed under low sunlight in winter, i.e., from December to January, with application of high concentration nitrogen, the flower-bud blasting was caused by the higher dry matter partition in the leaves and shoots than that in the flower bud.Key Words：abortion, assimilate, dry matter partition, soilless culture

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