Ethylene and the Growth of Rice Seedlings

Abstract

ABSTRACT?Etiolated whole rice seedlings enclosed in sealed vials produced ethylene at a rate of 0.9 picomole per hour per seedling. When 2-centimeterlong shoots were subdivided into 5-millimeter-long sections, the sections containing the tip of the shoot evolved 37% of the total ethylene with the remaining 63% being produced along a gradient decreasing to the base of the shoot. The tip of the coleoptile also had the highest level of the ethylene precursor 1-aminocyclopropane-l-carboxylic acid and of the ethylene-forming enzyme activity. Ethylene is one of the factors controlling coleoptile elongation. Decapitation of the seedling reduced ethylene evolution to one-third its original level and inhibited coleoptile growth. In short-term experiments, the growth rate of decapitated seedlings was restored to almost that of intact seedlings by application of ethylene at a concentration of 10 microliters per liter. Apart from ethylene, 02 also participates in the control of coleoptile growth. When rice seedlings were grown in a gas mixture of N2 and 02, the length of the coleoptiles reached a maximum at a concentration of 2.5% 02. Lower and higher concentrations of 02 reduced coleoptile growth. The effect of exogenous ethylene on coleoptile growth was also 02 dependent.A remarkable characteristic of the rice coleoptile is its ability to grow in an environment containing very low levels of 02 or no detectable amounts of 02 at all ( 13, 25). The capacity of this organ to grow under hypoxic conditions has been interpreted as an adaptation ofthe rice seedling to flooding conditions, allowing it to emerge from the water where the 02 concentration is much lower than in the air. This adaptive behavior seems to be shared by all cultivated species of the genus Oryza (13), including the wild rice, Zizania aquatica (2). Echinochloa crus-gaili ( 11) and Peltandra virginica (3) are also able to germinate and grow under hypoxic conditions. In low 02, the growth of rice seedlings is restricted to the coleoptile and mesocotyl while root and leaf growth is severely inhibited (22 NaOCI) for 10 min, followed by many rinses with tap and distilled H20.Germination. Seeds were germinated in darkness at 30± 0.2°C under two different conditions to vary coleoptile height. In most experiments, 1-cm-long coleoptiles were used which were obtained by germinating seeds in 14-cm Petri dishes containing 30 ml of distilled H20 for 2 to 3 d. In some experiments, longer coleoptiles (about 2 cm) were needed; these were obtained by germinating seeds in plastic boxes (20 x 10 x 8 cm) covered with 905 Reynolds plastic film. Six-hundred seeds and 20 ml of distilled H20 were placed in each plastic box, and the seedlings were grown for 6 d. Under these conditions, the coleoptiles grow taller because the duration of coleoptile growth is extended in sealed containers (see e.g. Raskin and Kende [ 18] Fig. 4). The whole seedling was placed in a glass chamber containing 1.5 ml of water, which was enough to cover half of the seed.Growth of Seedligs in Sealed and Flow-...

Ethylene-Induced Polyamine Accumulation in Rice (Oryza sativa L.) Coleoptiles

“…It has been established that ethylene can accelerate coleoptile elongation of etiolated rice seedlings (16,18,23). The present results from both sealed and aerobic conditions also support this finding.…”

“…In sealed containers, the accumulation of ethylene parelleled the increase in the elongation rate of coleoptiles. As in another report (23), the inhibition of the ethylene-enhanced coleoptile elongation by the specific inhibitor of ethylene action, 2,5-norbomadiene, indicates that ethylene plays a role in the stimulation of coleoptile elongation of etiolated rice seedlings. This conclusion is further supported by the stimulation of coleoptile elongation by ethylene and ACC in aerobic conditions.…”

Ethylene Plays Multiple Nonprimary Roles in Modulating the Gravitropic Response in Tomato1

“…Ethylene promotion of cell growth and elongation in the stem has also been reported for the aquatic plant Ranunculus sceleratus when submerged in water (Abeles et al, 1992), as well as for ethylene-treated etiolated rice coleoptiles (Satler and Kende, 1985). In the meadow grass Poa pratensis and oat, the ethylene-releasing compound ethephon has been implicated in the increase of tiller internode length (Abeles et al, 1992).…”

Involvement of Phenolic Compounds in Anaerobic Flooding Germination of Rice (<i>Oryza sativa</i> L.)

“…The role of ethylene hormone was mostly focused on in this complex process. Ethylene promotes the growth of coleoptile under deep water where oxygen concentration is in shortage, and higher ethylene levels mean faster and longer coleoptile elongation [5,14]. However, the mechanism of ethylene production under anoxic condition is unclear because oxygen is the main factor for activating the enzyme 1-aminocyclopropane-1-carboxylic acid in the process of ethylene synthesis [15].…”