Masaya Masumori

Effects of flooding on downstream processes of glycolysis and fermentation in roots of Melaleuca cajuputi seedlings

We investigated the energy metabolism in roots of flooded Melaleuca cajuputi Powell, a tropical flood-tolerant tree species, by measuring adenylate concentrations and activities of glycolytic and fermentative enzymes under flooded conditions. Adenylate energy charge (AEC) decreased slightly to 0.72 on the second day of flooding and recovered to around 0.8 by the fourth day of flooding. Activities of pyruvate decarboxylase (EC 4.1.1.1) and alcohol dehydrogenase (EC 1.1.1.1) increased initially and then decreased to the control level after 14 days of flooding. On the other hand, activities of pyruvate kinase (EC 2.7.1.40), phosphoenolpyruvate phosphatase (EC 3.1.3.2), and a series of phosphoenolpyruvate carboxylase (EC 4.1.1.31), malate dehydrogenase (EC 1.1.1.37), and NADP dependent malic enzyme (EC 1.1.1.40), which can convert PEP into pyruvate, were not induced in flooded roots throughout the experiment. These results suggest that neither the downstream reactions of glycolysis nor ATP production via glycolysis was enhanced by flooding, whereas alcohol fermentation was enhanced. With the low ATP yield of the glycolysis–alcohol fermentation pathway and no induction of glycolytic enzymes, the glycolysis–alcohol fermentation pathway itself contributes little to ATP production in flooded roots of M. cajuputi. These physiological responses of M. cajuputi to flooding may have the advantages of surviving flooded conditions because they can avoid exhaustion of sugar and accumulation of ethanol, a toxic end product of alcohol fermentation.

Growth Response of Melaleuca cajuputi to Flooding in a Tropical Peat Swamp

We investigated the growth response ofMelaleuca cajuputi Powell to flooding at 3 sites in a tropical swamp in southern Thailand. The relative growth rate (RGR) in height tended to be higher where the water level was higher. The maximumRGR in height was achieved during the flood period at the 2 sites where water levels were higher than at the other site. The height growth ofM. cajuputi was not reduced by flooding, but enhanced. No decline in growth due to post-anoxic injury was observed after flooding.Melaleuca cajuputi may have mechanisms to tolerate rhizospheric oxygen deficiency and to avoid post-anoxic injury.

Effects of evening and nighttime leaf wetting on stomatal behavior of Cryptomeria japonica growing in dry soil.

To examine the hypothesis that stomatal behavior of plants in dry soil is influenced by a slow recovery from daytime water deficit, we studied the effect of repeated wetting of leaves during evening and night in Cryptomeria japonica seedlings grown in dry soil. After 7 and 10 days of leaf wetting treatment the midday leaf water potential decreased and the transpiration rate increased, respectively. Therefore, we suggest that rapid recovery from daytime water deficit could weaken the water conserving stomatal behavior that adapts to drought conditions in the roots.

Radiocesium in Timber of Japanese Cedar and Japanese Red Pine, in the Forests of Minamisoma, Fukushima

The distribution of radiocesium within trees in the forests of Mimamisoma, Fukushima, Japan, was studied between 2012 and 2013 after the Fukushima Nuclear Power Plant accident. Most of the radiocesium was contained in the foliage and bark of the examined trees of Japanese cedar (Cryptomeria japonica) and Japanese red pine (Pinus densiflora), although considerable concentrations were detected in the xylem of C. japonica. At higher positions in the trunk, there was more radiocesium in heartwood than in sapwood. Radiocesium in the xylem of a tree with its root system removed before the nuclear accident suggests that most of the radiocesium was not transferred through the root system but was likely translocated via the foliage.

Photosynthetic limitation of similar-height Cryptomeria japonica trees growing at different rates

We compared light-saturated photosynthetic rates and their stomatal limitations among Cryptomeria japonica trees with a similar height but different current growth rates. Although slow-growing trees had a lower stomatal conductance and a higher carbon isotope ratio in shoots, the stomatal limitations in photosynthesis were not different. Large mesophyll CO2 diffusion resistance contributed to the low photosynthetic rate of the slow-growing trees.