Mesocotyl Growth Research Articles

Regulation of growth in rice seedlings

Etiolated rice seedlings (Oryza sativa L.) exhibited marked morphological differences when grown in sealed containers or in containers through which air was passed continuously. Enhancement of coleoptile and mesocotyl growth and inhibition of leaf and root growth in the sealed containers (“enclosure syndrome”) were accompanied by accumulation of CO2 and C2H4 in and depletion of O2 from the atmosphere. Ethylene (1 μl 1−1), high levels of CO2, and reduced levels of O2 contributed equally to the increase in coleoptile and mesocotyl growth. The effect of enclosure could be mimicked by passing a gas mixture of 3% O2, 82% N2, 15% CO2 (all v/v), and 1 μl l−1) C2H4 through the vials containing the etiolated seedlings. The effects of high CO2 and low O2 concentrations were not mediated through increased C2H4 production. The enclosure syndrome was also observed in rice seedlings grown under water either in darkness or in light. The length of the rice coleoptile was positively correlated with the depth of planting in water-saturated vermiculite. The length of coleoptiles of wheat, barley, and oats was not affected by the depth of planting. In rice, the length of coleoptile was determined by the levels of O2, CO2, and ethylene, rather than by light. This regulatory mechanism allows rice seedlings to grow out of shallow water in which the concentration of O2 is limiting.

Inhibitory action of red light on the growth of the maize mesocotyl: evaluation of the auxin hypothesis

Brief irradiation of 3-d-old maize (Zea mays L.) seedlings with red light (R; 180 J m(-2)) inhibits elongation of the mesocotyl (70-80% inhibition in 8 h) and reduces its indole-3-acetic acid (IAA) content. The reduction in IAA content, apparent within a few hours, is the result of a reduction in the supply of IAA from the coleoptile unit (which includes the shoot apex and primary leaves). The fluence-response relationship for the inhibition of mesocotyl growth by R and far-red light closely resemble those for the reduction of the IAA supply from the coleoptile. The relationship between the concentration of IAA (1-10 μM) supplied to the cut surface of the mesocotyl of seedlings with their coleoptile removed and the growth increment of the mesocotyl, measured after 4 h, is linear. The hypothesis that R inhibits mesocotyl growth mainly by reducing the IAA supply from the coleoptile is supported. However, mesocotyl growth in seedlings from which the coleoptiles have been removed is also inhibited by R (about 25% inhibition in 8 h). This inhibition is not related to changes in the IAA level, and not relieved by applied IAA. In intact seedlings, this effect may also participate in the inhibition of mesocotyl growth by R. Inhibition of cell division by R, whose mechanism is not known, will also result in reduced mesocotyl elongation especially in the long term (e.g. 24 h).

Phytochrome-controlled extension growth of Avena sativa L. seedlings

Fluence rate response curves for light-induced inhibition of mesocotyl growth and promotion of coleoptile growth in etiolated Avena sativa L. (cv. Victory) were developed. The irradiation time was 24 h. Fluence rates between 10(-6) and 10(5) nmol m(-2)s(-1) and 30 wavelengths between 563 and 1,093 nm were used. The main conclusions are as follows: 1. Both organs exhibit a low fluence rate response as well as a high fluence rate response. 2. The mesocotyl response is more sensitive to light than the coleoptile response. 3. The low fluence rate response of the mesocotyl shows a threshold of sensitivity at about 10(-7) nmol m(-2)s(-1) (i.e., total fluence of 5·10(-2) nmol m(-2) during the experiment) in the red and a saturation (about 70% inhibition of growth) at 10(-4) nmol m(-2)s(-1) (50 nmol m(-2)). 4. The action spectrum for the low fluence rate response parallels the Pr absorption spectrum. Alterations induced by screening are discussed. 5. The action spectrum demonstrates an exponential decrease in apparent photoconversion cross-section (Pr→Pfr) up to about 800 nm. Between 800 and 1,093 nm the photoconversion cross-section is only weakly dependent on wavelength. 6. The action spectrum for the high fluence rate response shows a broad peak in the red, a trough at 723 nm, and a sharp peak at 740-750 nm.

The photoperceptive sites and the function of tissue light‐piping in photomorphogenesis of etiolated oat seedlings*

Abstract. Responses to red light irradiation of discrete areas along the intact, etiolated oat seedling indicate that illumination of the region around the coleoptilar node results in maximal coleoptile growth stimulation and mesocotyl growth suppression. Quantitation of the fibre optic properties of these etiolated tissues shows that the amount of axially transmitted light is log linear as a function of distance for both the mesocotyl and coleoptile (plus primary leaf). Using the fibre optic properties of the tissues to predict the response of the etiolated seedling to defined illumination fields allows one to localize two sites of photoperception: although the mesocotyl response pattern can be explained by the action of a single site found near the top of the mesocotyl itself, the coleoptile response depends on irradiation of both the mesocotyl site and an additional site located just above the node. The very low‐ and the low‐fluence responses of etiolated oats independently predict similar regions of the seedling as sites of photo‐perception. The fibre optic properties of the seedling could allow the seedling to increase the effective light signal received by the photosensitive area significantly.

GERMINATION AND SEEDLING GROWTH IN ECHINOCHLOA CRUS‐GALLI VAR. ORYZICOLA UNDER ANOXIC CONDITIONS: STRUCTURAL ASPECTS

The morphological and cellular basis of anoxic germination in Echinochloa crus‐galli var. oryzicola is reported. The embryo of E. crus‐galli var. oryzicola is typically panicoid in its overall morphology, and is relatively large with a prominent coleoptile and mesocotyl. The response to anoxia is essentially the same in light and dark. Shoot growth occurs in both mesocotyl and coleoptile by cell elongation with no cell division. There is no emergence of the radicle without oxygen. Under anoxia the growth response is not the same as etiolation; there is no plumule elongation within the coleoptile, no protochlorophyll(ide) is found, and limited mesocotyl elongation occurs without oxygen. Air‐dark treatment after anoxic germination results in a typical etiolated morphological response, including a resumption of mesocotyl growth, elongation of the plumule within the coleoptile, and initiation of pigment synthesis. These results indicate the effects of anoxia are not permanent but rather limiting and reversible.

Germination and Seedling Growth in Echinochloa crus-galli var. oryzicola Under Anoxic Conditions: Structural Aspects

The morphological and cellular basis of anoxic germination in Echinochloa crus-galli var. oryzicola is reported. The embryo of E. crus-galli var. oryzicola is typically panicoid in its overall morphology, and is relatively large with a prominent coleoptile and mesocotyl. The response to anoxia is essentially the same in light and dark. Shoot growth occurs in both mesocotyl and coleoptile by cell elongation with no cell division. There is no emergence of the radicle without oxygen. Under anoxia the growth response is not the same as etiolation; there is no plumule elongation within the coleoptile, no protochlorophyll(ide) is found, and limited mesocotyl elongation occurs without oxygen. Air-dark treatment after anoxic germination results in a typical etiolated morphological response, including a resumption of mesocotyl growth, elongation of the plumule within the coleoptile, and initiation of pigment synthesis. These results indicate the effects of anoxia are not permanent but rather limiting and reversible.

Promotion of mesocotyl growth in etiolated rice seedlings by 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione

4-Ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione (TA) promoted mesocotyl growth in dark-grown rice (Oryza sativa L.) seedlings. In cultivars of the japonica type TA alone showed a small promotive effect and TA+gibberellic acid(GA3) had a marked synergistic effect, while in other cultivars, mostly of the indica type, TA alone showed a great promotive effect and TA+GA3 had only an additive effect. In cv. Nato, a typical representative of cultivars showing the second type of response, the concentration of TA giving the greatest growth promotion was around 0.1-0.2 mM. In Nato seedlings treated with TA at 0.1 mM, the mesocotyls continued to elongate for 6 days and reached about 75 mm in length, while the mesocotyls of control seedlings grew to a maximum of about 10 mm and growth was limited to the first 3 days after planting. The TA-induced mesocotyl elongation was mainly the consequence of increased cell multiplication in the meristematic area immediately below the coleoptilar node. GA3, abscisic acid (ABA) and ethylene also stimulated mesocotyl growth in dark-grown Nato seedlings but their effects were much smaller than those of TA. ABA, like GA3, had an additive effect with TA, but ethylene suppressed the effect of TA and resulted in increased lateral expansion in the upper region of the mesocotyls of TA-treated seedlings.

Adaptive Importance of Mesocotyl and Coleoptile Growth in Rice Under Different Moisture Regimes.

The lengths of mesocotyls (first internodes) and coleoptiles of rice varied greatly with the moisture content of the seed-bed. The optimum moisture content in most Indica cultivars was much higher for coleoptile than for mesocotyl growth, but not in some Japonica cultivars because the mesocotyl growth was not vigorous and did not vary with water content. Under submerged conditions, coleoptile growth was markedly stimulated, particularly in Japonica cultivars but there was no mesocotyl elongation in either cultivar. The plastic variability in the growth of coleoptile, leaves, mesocotyl and other internodes may be an adaptive response of rice to the water tension of the soil. Endogenous ethylene formation and effects of ethylene and carbon dioxide were also studied.

Auxin and Ethylene Control of Growth in Seedlings ofZea maysL. andAvena sativaL

The effects of applied ethylene on the growth of ooleoptiles and mesocotyls of etiolated monocot seedlings (oat and maize) have been compared with those on the epicotyl of a dicot seedling (the etiolated pea). Significant inhibition of elongation by ethylene ( 10 pi l1 for 24 h) was found in intact seed lings of all three species, but lateral expansion growth was observed only in the pea internode and oat mesocotyl tissue. The sensitivity of the growth of seedling parts to ethylene is in the decreasing order pea internode, oat coleoptile and oat mesocotyl, with maize exhibiting the least growth response. Although excised segments of mesocotyl and coleoptile or pea inter node all exhibit enhanced elongation growth in IAA solutions (10_6-2 x 10~5 mol 1_1), no consistent effects were found in ethylene. Ethylene production in segments was significantly enhanced by application of auxin (IAA, 10-5 mol 1_1 or less) in all tissues except those of the oat mesocotyl. Segments of maize show a slow rate of metabolism of applied [2-14C]IAA (30 per cent con verted to other metabolites within 9 h) and a high capacity for polar auxin transport. Ethylene (10 pi 1_1 for 24 h) has little effect, on either of these processes. The oat has a smaller capacity for polar transport than maize and the rate of metabolism of auxin is as fast as in the pea (90 per cent metabolized in 6 h). Although ethylene pretreatment does not change the rate of auxin metabolism in oat, there is a marked reduction in auxin transport. It is proposed that the insensitivity of maize seedlings to ethylene is related to the supply and persistence of auxin which could protect the seedling against the effects of applied or endogenously produced ethylene. Although the mesocotyl of oat is sensitive to applied ethylene it may be in part protected against ethylene in vivo by the absence of an auxin-enhanced ethylene production system. The results are discussed in relation to a model for the auxin and ethylene control of cell growth in the pea.

Studies on the Japanese Barnyard Millet as Soiling Crop : III. Mesocotyl elongation in Japanese barnyard millet seedling

The elongation of mesocotyl of Japanese barnyard millet (Echinochloa utilis Ohwi et Yabuno) seedling was remarkable and attained to about 13 cm, though the coleoptile was only about 0.5 cm in length at 30°C in the dark. Decapitation of coleoptile remarkably inhibited the elongation of mesocotyl in proportion to the extent of decapitation. Eluted sections of paper chromatograms from ether extract of coleoptiles of Japanese barnyard millet were used to characterize the growth response of wheat coleoptile sections. At Rf values of 0.1∼0.2, 0.4 and 0.9 in acid fraction an increase of wheat coleoptile elongation was observed, with the increase of 25∼45 per cent over the control. The effects of gibberellin (GA), indole-3-acetic acid (IAA), 2, 3, 5-triiodobenzoic acid (TIBA) and trans-cinnamic acid (TCA) on the growth of seedlings by treatment to sowing bed were tested. GA (1∼1OOppm) had no effect on elongation of mesocotyl. IAA had a little stimulation on the elongation of coleoptile with 10-6M, but mesocotyl elongation was inhibited with 10-5M and 10-6M. TIBA considerably increased the coleoptile elongation with 17.5 ppm, and conversely inhibited the mesocotyl elongation with the same concentration. TCA had also the same effect, although the effect was not remarkable as well as TIBA. GA(10∼1000 ppm) had no promotive effect on elongation of mesocotyl sections. IAA had promotive effect on elongation of mesocotyl sections at the concentration of 10-M and 10-6M. TIBA(1∼10 ppm) had an inhibitory effect on mesocotyl elongation and a stimulative effect on coleoptile elongation in the sections contained both coleoptile and mesocotyl. As the results of marking method and microscopic observation, it became clear that the growing region of mesocotyl was limitted narrow range of about 2 mm lower the coleoptilar node, and the growth of mesocotyl depend on the both cell division and cell elongation

RED LIGHT ENHANCES THE GROWTH OF AVENA COLEOPTILES

SUMMARY A 3 hours lasting irradiation with red light 27 hours after moistening of Avena seeds does not repress the growth of the mesocotyls completely. A second irradiation with red light 72 hours after moistening further reduces mesocotyl growth. In contrast red light enhances slightly but significantly the growth of the coleoptiles. Total seedling growth is reduced.

ON THE INHIBITION OF MESOCOTYL GROWTH BY ETHYLENE

SummaryOat seedlings have been treated with ethylene‐generating substances, (2‐chloroethyl)phos‐phonic acid (ethrel) and β‐hydroxyethylhydrazine (B‐OH), as well as with gaseous ethylene in an attempt to confirm the claim that mesocotyl growth can be stimulated by ethylene. The factorially arranged experiments included a standard exposure to light to permit evaluation of the light × ethylene interaction.Ethrel always inhibited growth and caused the malformations associated with ethylene treatment. In contrast, B‐OH brought about the ‘CO2 effect’; that is, mesocotyl growth was retarded at first but subsequently enhanced due to an increased number of cells having an unchanged final length, while the growth of the coleoptile was reduced. These plants showed no ethylene‐type distortions, however. As ethylene gas itself was invariably inhibitory it cannot be assigned any stimulatory properties at the concentrations used.One treatment combination (B‐OH with CO2) caused the death, selectively, of the tip cells of the coleoptile. Even without these cells, allegedly an essential part of the growth‐regulatory system of the seedling, a promotion of mesocotyl growth was observed.In the discussion support is deduced for the view that mesocotyl growth is not controlled by the tip of the coleoptile.

On the Growth Process of Rice Mesocotyl : II. Comparison of mesocotyl growth of seedlings among seeds of different locations in a panicle and between new and old seeds

It has been known that the mesocotyl of the japonica type of rice does not elongate more than 1 cm even in darkness. In the previous paper, however, it was shown that the mesocotyl of some seedlings of a japonica rice elongated more than 1 cm, whereas the mean mesocotyl length of total seedlings was less than 3 mm. Assuming that this variation of mesocotyl length may be caused by some physiological differences in the seeds, the following experiments were conducted. Rice seeds, Oryza sativa L. cv. Sasanishiki, belonging to the japonica type were used as materials. After harvesting, the panicles were dried 45 days under the room conditions in 1972. Seventy-two panicles with each 8 primary branches (Fig. 1) were selected for the experimental use. Terminal (I), middle (V) and lowest (VIII) branches were cut off at their bases. They were sterilized, washed and placed on a sheet of wet cotton wool, being incubated in darkness at 30°C for 11 days. The almost all seedlings of the terminal and the middle branches had short mesocotyls, whereas the some seedlings of the lowest (VIII) branches, especially located at 2' and 3' positions on secondary branches, produced long mesocotyls (Fig. 1, 2 and Table 1, 2). When the seeds located at 1, 2, 3, and 4 positions of the upper primary branches (x), and those located at 2', 3' and 4' positions of the lower secondary branches (●) were sampled (Fig. 1), and incubated separately in darkness at 30°C for 10 days, 4 % of the former and 50% of the latter plants produced long mesocotyls (more than 6 mm), respectively. The growth pattern of these plants with long mesocotyls was very similar to that of the plants treated with abscisic acid (ABA) as shown in the previous study (Fig. 2). The seeds harvested in the falls of 1970, 71 and 72, i.e. 2.1, 1.1 year and 1.5 month after harvest, respectively, were sterilized, and placed on a sheet of wet cotton wool in Petri dishes, being applied with or without 10 ppm of gibberellic acid (GA3), and were incubated in darkness at 30°C for 10 days. As shown in Fig. 3, a half of the 2.1 year seeds did not germinate, whereas almost all seeds germinated in both 1.1 year and 1.5 month seeds. In 2.1 year old seeds, the frequency of longer mesocotyls increased (Fig. 3). This mesocotyl, elongation was promoted by GA3 treatment, i.e. about one thirds of mesocotyls elongated to 15-36 mm in 2.1 year old seeds, while no mesocotyl reached over 15 mm in both current and 1.1 year old seeds. In this case too, the growth pattern of seedings with long mesocotyls was vas very similar to the plants treated with ABA (Fig. 4). From above results, it may be suggested that the variation in mesocotyl growth reflects the difference of some internal factors which are affected by the location of seed in a panicle or the time after the seed harvest.

Interaction between ethylene, abscisic acid and gibberellic acid in elongation of rice mesocotyl

Combined application of ethylene, abscisic acid and gibberellic acid produced marked partly synergistic stimulation of mesocotyl growth of japonica rice in darkness.

Abscisic Acid as a Stimulator for Rice Mesocotyl Growth

WHEN abscisic acid (ABA) is applied to a growing plant, it usually inhibits the growth of stem, leaf sheath and other plant parts1–3. Here I report the possibility that ABA stimulates the growth of rice mesocotyl in darkness.

Genetic Studies on the Emergence of Rice Seedlings in Direct Seeding Culture on Upland Field. : I. Diallel Cross Analysis on the Growth of Mesocotyl and Lower Internodes in Japonica Rice Seedlings

Genetic Studies on the Emergence of Rice Seedlings in Direct Seeding Culture on Upland Field. : I. Diallel Cross Analysis on the Growth of Mesocotyl and Lower Internodes in Japonica Rice Seedlings

Stimulation of oat and rice mesocotyl growth by ethylene

A low concentration of ethylene stimulated growth of intact oat and rice mesocotyls in darkness. Combined application of ethylene and gibberellin A3 produced an evident additive effect on the elongation of rice mesocotyls.

Phytochrome Changes Correlated to Mesocotyl Inhibition in Etiolated Avena Seedlings

The elongation of etiolated Avena mesocotyls is inhibited by red light (660 mmu). Immediately after exposing mesocotyl sections to varying doses of red light the ensuing concentrations of phytochrome in the far-red absorbing form (P(730)) were measured. The extent of mesocotyl inhibition observed 5 days later is proportional to the logarithm of P(730) concentration in mesocotyl tissue at the time of red light exposure.The inhibition of mesocotyl growth by red light can be reversed partially by subsequent exposure to far-red light (730 mmu). Increasing doses of far-red light result in decreasing concentrations of P(730) as compared with the original P(730) level due to the preceding red light exposure. The reduced mesocotyl inhibition of seedings which had been exposed to red and far-red light is proportional to the logarithm of P(730) concentration remaining in the tissue at the end of the two light exposures.This indicates that the same correlation exists between P(730) concentration and growth response whether the seedlings had been exposed to red light only or to red followed by far-red light.

Carbon dioxide fixation by auxin treated tissues

The relationship between CO2 fixation and growth is a matter of considerable interest. Molliard (6) was probably the first to report that CO2 is beneficial for the elongation of pea stems and lupin hypocotyls in darkness as well as in light. Very little attention was paid to this observation until Yamaki (13) demonstrated that a 100 to 200 % increase in elongation of Avena coleoptiles was effected when as little as 0.5 % CO2 was present in the experimental atmosphere. Similar promotions of growth in coleoptiles and internodes of Avena have also been obtained by Nitsch and Nitsch (8) in certain experiments. More recently Mer (4, 5) has shown that in intact seedlings a concentration of 5 % CO2 promoted mesocotyl growth but inhibited the extension growth of coleoptiles. This inhibition is overcome by nitrates supplied to the seedlings. An investigation was therefore undertaken to study the products of C1402 fixation in relation to auxininduced growth and inhibition in coleoptile sections as also in intact plants. This paper is concerned with a study of the changes occurring in the detached coleoptile. During the progress of this investigation a brief account of Yamaki's recent work was made available (14). His conditions were different from those employed by us but there is a large measure of agreement in the conclusions drawn, namely, that IAA stimulates CO. fixation and has a marked influence on the metabolism of the fixation products.

Control of Growth and Reproductive Processes by Red and Far-Red Light

The primary actions of low-intensity light in triggering the photoperiodic and photomorphogenic reactions in plants are discussed. Topics discussed include the photopericdic control of flowering; low-intensity light reactions; the control of lettuce seed germination by light; the control of hypocotyl heok unberding with light; control of leaf expansion by light; control of anthocyanin synthesis by light; the control of oat coleoptile and mesocotyl growth by light; the action spectra for red and far red control of growth responses; the blue portion of the action spectra; reactions in the red and far red reaction system; and proposed areas of research. 59 references. (C.H.)