Internodes Of Deepwater Rice Research Articles

Sequential elongation of internodes of deepwater rice at different water depths

Abstract Deepwater rice (DWR) was grown for four seasons in Thailand where fields were deeply flooded 50–80 days after seedling emergence. After flooding commenced, water levels increased at rates of 2–6 cm/day until reaching maximum depths of 1–3 m. The DWR plants survived by elongation of internodes, thus increasing plant height and keeping the foliage above water. The total number of internodes with marked elongation (5–30 cm) ranged from 14, where water reached a maximum of 1 m to 20 at 3 m maximum water depth, but the five uppermost appeared to elongate under the influence of reproduction rather than water level. New nodes were produced at intervals of 10–12 days, and the most recently formed internodes elongated. The number of internodes formed at the base of the stems during the dryland phase which did not elongate depended on the time of commencement of flooding, but plants appeared able to elongate after production of the fourth node. Grain-yield was not decreased in the deepest water.

Particles Associated with the Outer Epidermal Wall in Internodes of Deepwater Rice

Particles Associated with the Outer Epidermal Wall in Internodes of Deepwater Rice

The Biophysical Basis of Elongation Growth in Internodes of Deepwater Rice

Partial submergence induces rapid internodal elongation in deepwater rice (Oryza sativa L., cv Habiganj Aman II). We measured in vivo extensibility, tissue tension, hydraulic conductance and osmotic potential in the region of cell elongation in the uppermost internode. The in vivo extensibility of the internode, measured by stretching of living tissue with a custom-made constant stress extensiometer, rose rapidly following submergence of the plant. Both the elastic (E(el)) and plastic (E(pl)) extensibility increased when growth of the internode was induced. The submerged internode displayed tissue tension (elastic outward bending of longitudinally split internode sections); in air-grown control internodes, no such bending occurred. The hydraulic conductance, estimated from the kinetics of tissue shrinkage in 0.5 molar mannitol and subsequent swelling in distilled water, was not changed by submergence. The osmotic potential, measured with a dew-point hygrometer using frozen-thawed tissue, was only 18% less negative in the submerged internode than in the air-grown control. This indicates that osmoregulation takes place in rapidly elongating rice internodes. We suggest that the rapid expansion of the newly formed internodal cells of submerged plants is controlled by the yielding properties (E(pl)) of the cell walls. Experiments with excised stem sections indicate that gibberellin is involved in increasing the E(pl) of the elongating cell walls.

Amylase activity and growth in internodes of deepwater rice

Isoelectrofocusing, product analysis, thermal denaturation studies and affinity chromatography on cycloheptaamylose-Sephadex were used to identify the amylolytic enzymes in internodes of deepwater rice (Oryza sativa L.). Amylolytic activity in internodes of deepwater rice consists of α-amylase (sometimes separated into two isoforms) and of β-amylase. During submergence of whole plants, α-amylase activity increases in young, growing internodes, but β-amylase activity declines. Although non-growing, mature internodes contain higher levels of β-amylase than do the elongating younger internodes, the effect of submergence on amylase activities in both tissues follows the same trend. Submergence, gibberellic acid (GA3) and ethylene all promote α-amylase activity in growing and non-growing internodes of excised deepwater-rice stem sections. Inhibitor studies showed that submergence and ethylene promote α-amylase activity in the absence of endogenous gibberellin (GA), and GA3 enhances α-amylase activity when ethylene action is inhibited. Therefore, ethylene and GA appear to increase α-amylase activity independently of each other. Enhanced α-amylase activities are probably responsible for the mobilization of carbohydrates which are needed to support internode elongation during submergence of deepwater rice.

In Vivo 1-Aminocyclopropane-1-Carboxylate Synthase Activity in Internodes of Deepwater Rice

Inasmuch as the activity of 1-aminocyclopropane-1-carboxylate (ACC) synthase cannot be measured in homogenates of deepwater rice internodes (Oryza sativa L.), we have employed an in vivo assay to determine the activity of this enzyme. This assay is based on the accumulation of ACC in tissue kept under N(2). Submergence of whole plants or stem sections containing the uppermost, developing internode enhances the in vivo activity of ACC synthase in the stem. This stimulation of in vivo ACC-synthase activity is especially pronounced in the region of the internode containing the intercalary meristem and the elongation zone above it. Enhancement of in vivo ACC-synthase activity is evident after 2 hours of submergence and shows a peak after 4 hours. Reduced levels of atmospheric O(2), which promote ethylene synthesis and growth in internodes of deepwater rice, also enhance the in vivo activity of ACC synthase. Our results are consistent with the hypothesis that induction of ACC-synthase activity at low partial O(2) pressures is among the first biochemical events leading to internodal growth in deepwater rice.

The effect of submergence, ethylene and gibberellin on polyamines and their biosynthetic enzymes in deepwater-rice internodes

Submergence and treatment with ethylene or gibberellic acid (GA3) stimulates rapid growth in internodes of deepwater rice (Oryza sativa L. cv. "Habiganj Aman II"). This growth is based on greatly enhanced rate of cell-division activity in the intercalary meristem (IM) and on increased cell elongation. We chose polyamine biosynthesis as a biochemical marker for cell-division activity in the IM of rice stems. Upon submergence of the plant, the activity of S-adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) in the IM increased six- to tenfold within 8 h; thereafter, SAMDC activity declined. Arginine decarboxylase (ADC; EC 4.1.1.19) showed a similar but less pronounced increase in activity. The activity of ornithine decarboxylase (ODC; EC 4.1.1.17) in the IM was not affected by submergence. The levels of putrescine and spermidine also rose in the IM of submerged, whole plants while the concentration of spermine remained low. The increase in SAMDC activity was localized in the IM while the activity of ADC rose both in the node and the IM above it. The node also contained low levels of ODC activity which increased slightly following submergence. Increased activities of polyamine-synthesizing enzymes in the nodal region of submerged plants probably resulted from the promotion of adventitious root formation in the node. Treatment of excised rice-stem sections with ethylene or GA3 enhanced the activities of SAMDC and ADC in the IM and inhibited the decline in the levels of putrescine and spermidine. We conclude that SAMDC and perhaps also ADC may serve as biochemical markers for the enhancement of cell-division activity in the IM of deepwater rice.

A Comparison of the Submergence Response of Deepwater and Non-Deepwater Rice

Twelve cultivars of rice (Oryza sativa L.), representing deepwater, short-statured, and semidwarf types, were tested for their response to submergence. The magnitude of the response varied between cultivars; however, all cultivars responded to submergence by rapid growth once internodal elongation had started. Three of these cultivars were tested for elongation capacity at four ages. The deepwater rice was capable of rapid internodal elongation in response to submergence at 4 weeks of age. Growth of the short-statured and semidwarf cultivars was not stimulated by submergence until about 10 weeks of age. In air, the internodes of deepwater rice grew slower than did those of the short-statured and semidwarf cultivars. We also investigated the elongation response of stem sections of all 12 cultivars to an atmosphere containing 3% O(2), 6% CO(2), 91% N(2) (all by volume), and 1 microliter per liter ethylene. We found that the response of each of the non-deepwater cultivars was qualitatively and quantitatively similar to that of the deepwater rice.

Effect of Stem Borer (Sb) At Different Internodes of Deep Water Rice

Effect of Stem Borer (Sb) At Different Internodes of Deep Water Rice

Effect of Submergence on the Cell Wall Composition of Deep-Water Rice Internodes

The cell wall composition of internodes of deep-water rice plants (Oryza sativa L. cv Habiganj Aman II) which were induced to grow rapidly by submergence in water was compared to that of nonsubmerged plants which grew slowly. No differences could be detected in cellulose, uronic acid, and lignin content expressed on a dry weight basis. Cell wall preparations of rapidly growing, submerged internodes contained more hydroxyproline and had a higher hydration capacity than those of control internodes. The silicon content of submerged rice internodes was considerably lower than that of air-grown plants. The role of silicon as a structural component of the cell wall of grasses is discussed in relation to lodging of deep-water rice plants after the flood waters have receded.