Shoji Tachibana

Effect of supraoptimal root temperature on the growth, root respiration and sugar content of cucumber plants

Abstract The effects of high root temperature on plant growth, leaf elemental composition, root respiration and sugar content in cucumber plants (Cucumis sativus L. cultivar ‘Sharp I’) were studied. Root dry weight, leaf area and leaf concentrations of most nutrient elements were all reduced as the root temperature was raised to 35°C, and to 38°C in particular. High root temperature markedly enhanced intact root respiration. This increase of root respiration was due to the stimulation of the alternative respiration. On the other hand, the cytochrome respiration deteriorated at high root temperatures. However, ATP content was not much different between the roots grown at 25° and 38°C. With the rise of root temperature, root sugars, particularly raffinose, greatly increased, while root pectin content decreased. High root temperature also adversely affected the levels of malic and fumaric acids in the roots. It is suggested that disturbance of carbohydrate metabolism in the root is a primary factor responsible for the growth inhibition and dysfunctions of cucumber roots grown at supraoptimal root temperatures.

Ameliorative effect of polyamines on the high temperature inhibition of in vitro pollen germination in tomato (Lycopersicon esculentum Mill.)

Effect of polyamines on in vitro pollen germination at high temperatures in tomato (Lycopersicon esculentum Mill.) was investigated. Pollen germination and tube growth were significantly inhibited at 33°C and 35°C compared to those at 25°C. This inhibition was reversed by the addition of spermidine or spermine in the germination medium. Spermidine at 0.5 mM was slightly more effective than spermine at 0.05 mM. Spermidine at 0.05 and 0.5 mM and spermine at 0.05 mM slightly increased pollen germination rates at 25°C. Spermidine at 5 mM and spermine at 0.5 M were inhibitory to pollen germination, regardless of incubation temperatures. Spermidine also promoted germination of pollen grains incubated at 38°C for 1 and 3 h and then at 25°C for the rest of the 20 h incubation period. The effect was higher at 0.5 mM than at 0.05 mM. Treatment of spermidine to intact flowers 1 day before anthesis was also effective in ameliorating the high temperature inhibition of in vitro pollen germination on the polyamine-free medium. Here, the optimum concentration was 5 mM. These results demonstrate that polyamines can counteract the inhibitory effects of high temperature on pollen germination. They also suggest that the endogenous level of polyamines in germinating pollen grains is an important factor for the pollen germinability at high temperature.

Import of calcium by tomato fruit in relation to the day-night periodicity

Abstract The day-night periodicity in calcium (Ca) transport into fruits of tomato ( Lycopersicon esculentum Mill.) was investigated by growing plants with two trusses in aerated nutrient solution labelled with 45 Ca for 11 h either during the day or at night. The import of Ca by tomato fruits was favoured at night, although it also occurred during the day, but at a much lower rate. The rates of Ca absorption and translocation from roots to shoots did not differ between the day and the night. Withholding the oxygen supply to roots at night, which is a cause of blossom-end rot of tomato fruits in hydroponics, greatly inhibited both the absorption of Ca from roots to shoots.