Gametophyte contribution to sporophyte growth on the basis of carbon gain in the fern Thelypteris palustris: effect of gametophyte organic-matter production on sporophytes.

At an early stage of growth gametophytes support the sporophytes of ferns. Young sporophytes become independent of gametophytes when the first leaves develop. Although large fern gametophytes produce multiple archegonia simultaneously, only one sporophyte is typically established on one gametophyte. The number of sporophytes is believed to be controlled in two possible directions, from gametophyte to sporophyte or from preceding sporophyte to another sporophyte. To investigate the effects of gametophytes on their sporophytes, we studied the relationship between organic matter production by gametophytes and the growth of young sporophytes of Thelypteris palustris. We cut gametophytes in half (CGs) to reduce the gametophytes' production of matter. There was no significant difference between the growth of sporophytes on intact gametophytes (IGs) and that on CGs. According to our estimates, based on the rate of organic matter production, the large gametophyte was able to produce two or more sporophytes. The resources required for CGs to make similar-sized sporophytes was twice that for IGs. In polyembryony each of the multiple sporophytes was similar in size to the single sporophytes. Resource limitation does not seem to explain why fern gametophytes establish single sporophytes.

Tubers and rhizome fragments as propagules: competence for vegetative reproduction in Equisetum arvense.

Rhizome fragments (referred to as "fragments") and tubers of Equisetum arvense L. were cultured in order to investigate their competence with respect to vegetative reproduction. The starch concentration of the fragments was lower than that of the tubers, but the initial growth of new individuals from these fragments was superior to that from tubers obtained from the same dry mass. This superior growth was due to the large number of buds (grown from nodes) and aerial shoots on the fragments. The competence for vegetative reproduction depended on the relationship between the stored starch and the number of buds.

Response of non-structural carbohydrate content of belowground parts in Equisetum arvense according to the irradiance change during a growing season.

Effects of shading on the growth of Equisetum arvense during the growing season were studied in terms of the dynamics of non-structural carbohydrates (starch, sucrose, glucose). Tubers of 0.04 g dry mass were planted in pots. Plants were cultivated under different radiation conditions (100%, 3%, 100%-->3%, and 100%-->3%-->100%). The carbohydrate concentration in belowground parts responded sharply to the irradiance conditions. Under 3% relative photon flux density (PFD), they could not grow beyond the initial mass and decayed. Dry mass per length of rhizomes was highly correlated with the starch concentration, which was correlated with the mass of current tubers. The rhizomes of low starch concentration did not form current tubers. The carbohydrate concentration of rhizomes increased when the plants were transferred from 3% relative PFD to 100% irradiance conditions. After ca. 2 months of improved PFD, they had the same content of non-structural carbohydrates as the 100% PFD plants.

Two types of matter economy for the wintering of evergreen shrubs in regions of heavy snowfall.

Plant adaptation to an environment subject to heavy snowfalls was investigated in four species of evergreen shrubs growing in a Fagus crenata forest in an area of Honshu on the Sea of Japan. These shrubs stored carbohydrates in some organs before the snowy season and were covered with snow for 4-5 months. Aucuba japonica var. borealis, Camellia rusticana, and Ilex crenata var. paludosa maintained a reserve of carbohydrates during the snowy season. In Daphniphyllum macropodum var. humile, the reserve of carbohydrates decreased during winter. The respiration rates in the first three species decreased from autumn to winter, whereas the decrease in D. macropodum was slight. It was found that the first three species could use reserve carbohydrates for the growth of new shoots after the thaw, whereas in the last species the growth of new shoots depends on high photosynthetic activity in late spring. Our findings suggest some types of matter economy in evergreen shrubs for wintering in an environment of heavy snow.

Growth and photosynthesis of Japanese flowering cherry under simulated microgravity conditions.

The photosynthetic rate, the leaf characteristics related to photosynthesis, such as the chlorophyll content, chlorophyll a/b ratio and density of the stomata, the leaf area and the dry weight in seedlings of Japanese flowering cherry grown under normal gravity and simulated microgravity conditions were examined. No significant differences were found in the photosynthetic rates between the two conditions. Moreover, leaf characteristics such as the chlorophyll content, chlorophyll a/b ratio and density of the stomata in the seedlings grown under the simulated microgravity condition were not affected. However, the photosynthetic product of the whole seedling under the simulated microgravity condition increased compared with the control due to its leaf area increase. The results suggest that dynamic gravitational stimulus controls the partitioning of the products of photosynthesis.