Hiroshi Suge

Hydrotropism in roots: sensing of a gradient in water potential by the root cap

Roots of the agravitropic pea (Pisum sativum L.) mutant, ageotropum, responded to a gradient in water potential as small as 0.5 MPa by growing toward the higher water potential. This positive response occurred when a sorbitol-containing agar block was unilaterally applied to the root cap but not when applied to the elongation region. Unilateral application of higher concentrations of sorbitol to the elongation region caused root curvature toward the sorbitol source, presumably because of growth reduction on the water-stressed side. The control blocks of plain agar applied to either the root cap or the elongation region did not cause significant curvature of the roots. These results demonstrate that hydrotropism in roots occurs following perception of a gradient in water potential by the root cap.

Induction of hydrotropism in clinorotated seedling roots of Alaska pea,Pisum sativum L.

Roots of the agravitropic pea (Pisum sativum L.) mutantageotropum show positive hydrotropism, whereas roots of Alaska peas are hydrotropically almost non-responsive. When the gravitropic response was nullified by rotation on clinostats, however, roots of Alaska peas showed unequivocal positive hydrotropism in response to a water potential gradlent. These results suggest that roots of Alaska peas possess normal ability to respond hydrotropically and their weak hydrotropic response results from a counteracting effect of gravitropism.

Ethylene-light relationship in the growth of the rice coleoptile

SummaryEthylene stimulated growth of rice coleoptiles in the dark and after an irradiation with red light. The red-light inhibition of rice-coleoptile growth was more pronounced when only endogenously evolved C2H4 was involved than it was under C2H4-free (C2H4 removed) or C2H4-saturated (20 ppm C2H4 added) conditions.

Lazy gene (la) responsible for both an agravitropism of seedlings and lazy habit of tiller growth in rice (Oryza sativa L.)

Using an isogenic line of rice having lazy gene (la), we studied the correlation between the agravitropic response at the young seedling stage and the lazy habit (prostrate growth of tillers) at the more advanced stage of growth. In this study, it was found that both agravitropism and lazy habit were controlled by the single recessivela gene. That is, F2 segregants of Kamenoo×lazy-Kamenoo, which had an agravitropic response at their young seedling stage, showed a lazy habit of growth in the more advanced stage of vegetative growth. On the other hand, seedlings that showed normal gravitropic curvature at their early stage of growth had an upright growth in the mature stage.

Role of gravitropic response in the dry matter production of rice(Oryza sativa L. ) : an experiment with a line having lazy gene.

Role of gravitropic response in the dry matter production was explored using a near isogenic line pair of rice; Kamenoo and lazy-Kamenoo. Productive structures were quite different in plant with a lazy gene, lazy-Kamenoo from in Kamenoo. Heads were oriented in the surface of canopy in Kamenoo, while they distributed in all zones from the soil surface to the top of canopy in lazy-Kamenoo. The value of SLA, ratio of leaf area to leaf weight, was the same at the early stage of growth between Kamenoo and lazy-Kamenoo. However the value rapidly decreased in lazy-Kamenoo indicating that the thickness of leaves increased more rapidly with the advance of growth in plants with the lazy-gene. Tiller shoots of lazy-Kamenoo, showed prostrate or spreading growth pattern. This is probably due to the inability or reduced responsibility to gravity since they showed only reduced response to gravistimulation in 12-and 13-leaf stage and almost no response was detected in 14-leaf stage. On the other hand, Kamenoo well responded to gravistimulation in all growth stages tested. Thus, the difference in productive structure in two near isogenic lines was explained, at least in part, by their difference in gravitropic response.

Agravitropic growth and its relation to the formation of the plumular hook in etiolated shoots of the pea mutant, Ageotropum

Summary Shoots of a pea mutant, ageotropum ( Pisum sativum L.) exhibited agravitropic growth and less ability to form a plumular hook in the dark. Decapitated epicotyls of dark-grown ageotropum pea bent away from external IAA when applied to the cut-end asymmetrically. But symmetrical application of IAA to the entire cut-surface of the horizontally placed epicotyls could not induce gravitropic curvature. In horizontally placed epicotyls of dark-grown ageotropum pea, 3 H label applied as 3 HIAA moved basipetally but did not apparently move laterally. Seedlings of ageotropum pea formed the plumular hook to some extent in response to externally applied ethylene. Alaska (normal) epicotyls evolved 2 to 5 times more ethylene than ageotropum epicotyls. Gravistimulation of the shoots increased ethylene evolution in Alaska epicotyls but not in ageotropum epicotyls. These results suggest a positive correlation between auxin asymmetry and ethylene production, which may influence both shoot gravitropism and formation of the plumular hook.

Gravimorphism in rice and barley: promotion of leaf elongation by vertical inversion in agravitropically growing plants.

We have compared shoot responses of agravitropic rice and barley plants to vertical inversion with those of normal ones. When rice plants were vertically inverted, the main stems of a japonica type of rice, cv. Kamenoo, showed negative gravitropism at nodes 2–15 of both elongated and non-elongated intermodes. However, shoots of lazy line of rice, lazy-Kamenoo, bent gravitropically at nodes 11–15 only elongated internodes but not at nodes 2–10 of non-elongated ones. Thus, shoots of Kamenoo responded gravitropically at all stages of growth, whereas shoots of lazy-Kamenoo did not show gravitropic response before heading. In Kamenoo plants, lengths of both leaf-sheath and leaf-blade were shortened by vertical inversion, but those of the vertically inverted plants of lazy-Kamenoo were significantly longer than the plants in an upright position. When agravitropic and normal plants of barley were vertically inverted, the same results as in rice were obtained; elongation of both leaf-sheath and leaf-blade was inhibited in normal barley plants, Chikurin-Ibaragi No. 1, but significantly stimulated in agravitropic plants ofserpentina barley. These results suggest that vertical inversion of rice and barley plants enhances the elongation growth of leaves in the absence of tropistic response.

Responses of the first internodes of Hong Mang Mai wheat to ethylene, gibberellins and potassium

Abstract Seedlings of Hong Mang Mai wheat ( Triticum aestivum L.) emerge from much deeper in the soil than do other cultivars by elongating their first internode. We examined the roles of ethylene, gibberellins (GA) and potassium in the elongation of the first internode in wheat cultivars. Although ethylene stimulated the elongation of the first internode of Hong Mang Mai in the dark, the ethylene evolution and the expression level of ethylene-receptor-like gene of this cultivar were not greater than those of other cultivars. In Hong Mang Mai, gibberellin A3 (GA3) substantially stimulated the elongation of the first internode in the dark. Maximum elongation of the first internode was obtained by GA3 at the concentrations of 2.89 × 10–6 to 2.89 × 10–7 M. This cultivar responded markedly to gibberellins A1 and A3 by elongating the first internode in the dark. A mixture of gibberellins A4 and A7 (GA4+7) was not effective in inducing the elongation. Haruhikari, a cultivar having no GA -insensitive-reducing-height (Rht) genes, substantially responded to GA3, but other cultivars did not. The differences in the sensitivity to GA could account, at least in part, for the varietal differences in the elongation of the first internode in wheat. Takune-komugi, a cultivar whose first internode elongates in response to ethylene, did not respond to GA3. Thus, there are different mechanisms for the GA- and ethylene-stimulated elongation of the first internode in wheat. Also, it was suggested that potassium uptake from the soil might function together with endogenous GA in inducing the elongation of the first internode in Hong Mang Mai wheat.

Chapter 6 Gravitropic Mutants in Studying Plant Growth in Space

Publisher Summary Terrestrial organisms, including plants, have evolved under a prevailing 1-G gravity ever since their appearance on the planet earth. As a result, plants now positively respond to gravity for controlling their growth and development. The clinostat has long been used to compensate the unilateral influence of gravity and to simulate the responses of spacegrown plants. It has been argued that clinorotation of plants mimics the behavior of plants grown under microgravity. This physiological simulation of microgravity could be meaningful, particularly when the gravistimulus perceived by plants is reduced to near zero by using a clinostat with two axes perpendicular to each other. Another approach to the simulation of microgravity is the use of mutants insensitive to gravity or with a modified graviresponsiveness. This genetic approach should provide significant information on how plants respond to microgravity conditions and grow in space. This chapter describes the use of gravitropic mutants as a tool for understanding plant responses to gravity and space environment. These mutants may also give an idea about how plant growth can be practically accomplished in a “space farm.”

Physiological and ecological studies on the pond weed, Potamogeton distinctus A. Bennett, a perennial weed of paddy fields. III. Intraspecific variation in the morphology and cluster of winter buds.

鱗茎および鱗茎群 (1本の地下茎先端に隣接して着生する鱗茎のひとまとまり) の形態について, 全国より集めた12系統間の差異を比較検討した。鱗茎群当たりの着生鱗茎数, それを構成する1本の鱗茎の重さ・鱗茎間の着生間隔などの諸形質について著しい種内変異の存在が認められた。また, ポット当たりの形成鱗茎数では, 福岡産の系統が最も多く, 宮城産のものが最も少なく, 繁殖力に関する系統間変異も大きいことが示唆された。しかし, このような変異と各系統の産地の地理的位置との関係は明らかでなかった。