Substances with cytokinin activity in apple shoots during the vegetative season

The content of naturally occurring free substances with cytokinin activity was investigated in growing apices of apple shoots during the vegetative period. In the end of May one substance with cytokinin activity was found. During the first period of growth activity we found three such substances with more hydrophobic behaviour and in the culmination of the second period of growth activity we found other three or four substances displaying on the chromatogram more hydrophylic behaviour.     

Phyllotaxis of vegetative shoots, lamina rotation and their systematic implication in Magnoliaceae

Phyllotaxis in vegetative shoots and lamina rotation of Magnoliaceae are described. Most genera in Magnoliaceae investigated (except Parakmeria , Manglietiastrum and Pachylarnax ) show lamina rotation. Paraphoric, a new type of lamina rotation differing from four other types depicted by Charlton is clarified. Manglietia , Parakmeria , Manglietiastrum , Talauma , section Gwillimia and Rytidospermum in subgenus Magnolia , shoots of Woonyoungia , section Theorhodon and Liriodendron have spiral phyllotaxis, however Magnolia section Oyama and Maingol a, Alcimandra , Michelia , Paramichelia , Tsoogiodendron , buds of Woonyoungia , section Theorhodon and Liriodendron have distichous phyllotaxis. The systematic implication of vegetative shoot phyllotaxis and lamina rotation in Magnoliaceae is discussed in this paper.     

A transporter regulating silicon distribution in rice shoots

Rice (Oryza sativa) accumulates very high concentrations of silicon (Si) in the shoots, and the deposition of Si as amorphous silica helps plants to overcome biotic and abiotic stresses. Here, we describe a transporter, Lsi6, which is involved in the distribution of Si in the shoots. Lsi6 belongs to the nodulin-26 intrinsic protein III subgroup of aquaporins and is permeable to silicic acid. Lsi6 is expressed in the leaf sheath and leaf blades as well as in the root tips. Cellular localization studies revealed that Lsi6 is found in the xylem parenchyma cells of the leaf sheath and leaf blades. Moreover, Lsi6 showed polar localization at the side facing toward the vessel. Knockdown of Lsi6 did not affect the uptake of Si by the roots but resulted in disordered deposition of silica in the shoots and increased excretion of Si in the guttation fluid. These results indicate that Lsi6 is a transporter responsible for the transport of Si out of the xylem and subsequently affects the distribution of Si in the leaf.     

Seasonal fluctuations of vegetative growth in roots and shoots of central Chilean shrubs

Summary Seasonal growth dynamics of the root and shoot systems of dominant shrubs of the Chilean matorral were studied. In some species root and shoot activity were synchronous, while in others production of fine roots was observed prior to bud burst and shoot elongation. Biomass production of new roots was significantly higher in spring than in autumn. Maximum biomass of dead roots was concomitant with the maximum amounts of litter under the canopy.     

RNAi-mediated disruption of squalene synthase improves drought tolerance and yield in rice

About one-third of the world's rice area is in rain-fed lowlands and most are prone to water shortage. The identification of genes imparting tolerance to drought in the model cereal plant, rice, is an attractive strategy to engineer improved drought tolerance not only rice but other cereals as well. It is demonstrated that RNAi-mediated disruption of a rice farnesyltransferase/squalene synthase (SQS) by maize squalene synthase improves drought tolerance at both the vegetative and reproductive stages. Twenty-day-old seedlings of wild type (Nipponbare) and seven independent events of transgenic RNAi lines showed no difference in morphology. When subjected to water stress for a period of 32 d under growth chamber conditions, transgenic positives showed delayed wilting, conserved more soil water, and improved recovery. When five independent events along with wild-type plants were subjected to drought at the reproductive stage under greenhouse conditions, the transgenic plants lost water more slowly compared with the wild type, through reduced stomatal conductance and the retention of high leaf relative water content (RWC). After 28 d of slow progressive soil drying, transgenic plants recovered better and flowered earlier than wild-type plants. The yield of water-stressed transgenic positive plants ranged from 14-39% higher than wild-type plants. When grown in plates with Yoshida's nutrient solution with 1.2% agar, transgenic positives from three independent events showed increased root length and an enhanced number of lateral roots. The RNAi-mediated inactivation produced reduced stomatal conductance and subsequent drought tolerance.     

Role of rice PPS in late vegetative and reproductive growth

The rice peter pan syndrome-1 (pps-1) mutant shows a prolonged juvenile phase and early flowering. Although the early vegetative phase and flowering time of pps-1 have been closely examined, the phenotypes in the late vegetative and reproductive phases are not yet well understood. In the ninth leaf blade of pps-1, the relative length of the midrib was comparable to the sixth leaf blade of wild-type. Moreover, pps-1 had a small inflorescence meristem and small panicles. These phenotypes indicate that in pps-1 the juvenile phase coexists with the late vegetative phase, resulting in small panicles. Gibberellin is known to promote the juvenile-adult phase transition. d18-k is dwarf and has a prolonged juvenile phase. Double mutant (d18-k pps-1) showed the same phenotype as the pps-1, indicating that PPS is upstream of GA biosynthetic genes.     

Induction ofent-kaurene biosynthesis by low temperature in dwarf peas

Germinating pea (Pisum sativum L.) seeds of two dwarf cultivars, “Progress No. 9” and “Green Arrow”, and two tall cultivars, “Alaska” and “Alderman”, were treated with low temperature (3–5°C) for 14 days and then transferred to normal growing conditions (19–21°C for 16 h/14.5–16.5°C for 8 h) for an additional 10 days. Biosynthesis of [¹⁴C]ent-kaurene from [¹⁴C]2-mevalonic acid (2-MVA) was assayed in cell-free enzyme extracts prepared from shoot tips 10 days after cold treatment and was compared with activity in enzyme extracts prepared from noncold-treated, 10-day-old control plants. Shoot lengths of cold-treated plants were measured throughout a 35-day period and compared with shoot lengths of plants grown without cold treatment for 25–35 days. Low temperature induced a five-to 10-fold enhancement ofent-kaurene, hence potentially gibberellin (GA), biosynthesis in seedlings of the two dwarf cultivars but not in the tall cultivars. However, the lack of an increase in growth rate in the cold-treated dwarfs indicated that endogenous GA biosynthesis remained blocked at some point beyondent-kaurene in the biosynthetic pathway. Since the late-flowering “Alderman” cultivar did not exhibit enhanced biosynthesis ofent-kaurene, it appears that if vernalization in late-flowering cultivars of peas is correlated with enhanced GA biosynthesis, it is not the early part of the biosynthetic pathway which is affected.     

Organogenesis of vegetative shoots from in vitro cultured flower buds of Mammillaria albicoma (Cactaceae)

We tested the organogenetic capacity of floral buds of Mammillaria albicoma Böed. (Cactaceae). Buds were incubated on solid MS medium supplemented with 0.1 mg l^?1 α-naphthaleneacetic acid (NAA) and 5.0 mg l^?1 6-benzylaminopurine (BA). Callus growth was observed from the cut explant base and from within the perianth. These calli during subsequent subcultures to the same medium gave rise to adventitious shoots. Shoots formed also directly from the perianth, as confirmed by observations in the light microscope and scanning electron microscope (SEM). On transfer to a fresh medium, the shoots produced proliferating cultures. This is the first report of regeneration of cactus shoots from floral explants.     

Ozone exposure during growth affects the feeding value of rice shoots

Rising tropospheric ozone concentrations have been observed in many Asian countries in recent years. Ozone pollution reduces the yield of agricultural crops but may also affect crop quality. This study aimed at estimating the effect of ozone exposure on feeding quality of rice shoots for ruminant herbivores. Rice plants from two genotypes differing in ozone tolerance were exposed to ozone at a concentration of 120 nl/l for 18 days, and feeding value was determined by chemical analyses and in vitro incubation in rumen fluid. Rice biomass was reduced by an average of 24% in the ozone treatment as compared to the control. Moreover, ozone exposure affected various feed quality parameters. Crude protein content was lower in ozone treated plants (P<0.05). Potential gas production during the in vitro incubation for 96 h also dropped (P<0.01) due to ozone treatment, indicating reduced digestibility of the plant materials. This was explained with an increase in the antinutritive components lignin (P<0.05) and phenolics (P<0.001) due to ozone exposure. An ozone tolerant genotype exhibited a more pronounced increase in phenolics, suggesting that this may constitute a stress defense mechanism. Our results suggest that ozone may affect the feeding value of cereal straws and calls for further research in this direction.     

Purification and characterization of an alkaline invertase from shoots of etiolated rice seedlings

One alkaline invertase and two acid invertase activities were detected in the shoots of etiolated rice ( Oryza sativa ) seedlings. The alkaline invertase (AIT) was purified to homogeneity through steps of ammonium sulphate fractionation, concanavalin A-Sepharose affinity chromatography (non-retained), DEAE-Sephacel chromatography and preparative electrophoresis. The pH optimum of AIT was 7.0 and the molecular mass, determined by gel filtration, was 240 kDa. It is apparently a homotetrameric enzyme (subunit molecular mass 60 kDa). The isoelectric point was 4.4 by isoelectric focusing. The best substrate of the enzyme was sucrose, with a K _m of 2.53 mM. The enzyme also hydrolysed raffinose, but not maltose or lactose, so it is a β-D-fructofuranosidase. It gave negative glycoprotein staining. Of the hydrolysis products, fructose was a competitive inhibitor and glucose was a non-competitive inhibitor. Treatment with an alkaline phosphatase could activate AIT, whereas other proteins such as BSA, concanavalin A and urease had no effect on the enzyme activity. The enzyme activity was inhibited by Tris, thiol reagents and heavy metal ions.     

Dynamics and some characteristics of natural free cytokinin content in growing apices of apple tree shoots during the vegetative season

The changes of content and some chromatographic characteristics and biological activities of natural free cytokinins were studied during the vegetation season in the growing apices of apple tree shoots. Biological cytokinin activity was discovered in two groups of compounds differing in the time of their biological actions. Rf values and in the time of their maximal content in the growing apices. The time of maximal content was in accordance with their biological activity.     

褐飞虱和白背飞虱的取食为害对水稻营养生长的影响

对塑料钵栽培的水稻进行罩宠试验,研究了褐飞虱和白背飞虱在不同若虫密度下取食为害对水稻营养生长的影响．结果表明,两种飞虱的成虫干重、水稻叶面积和其地上部干重因若虫密度的增加而下降．叶片干重占地上部干重的比例和稻株分配给叶片干物质量随为害程度的加重而增大;褐飞虱和白背飞虱总干重（X）与稻株地上部损失量（Y）之间存在着极显著的线性关系．两种飞虱干重每增加1mg,水稻地上部干重则分别损失26.01mg和21．90mg．讨论了稻飞虱取食为害对水稻致害的可能机制．     

Localization of cells containing sedimented amyloplasts in the shoots of normal and lazy rice seedlings.

We have examined the localization of the cells containing sedimented amyloplasts (putative statocytes) and its relation to the graviresponding sites in the shoots of normal and lazy rice seedlings. All graviresponsive organs of the shoots of normal rice seedlings, the mesocotyl, the coleoptile and the leaf-sheath base, were found to possess the statocytes. This is the first indication that mesocotyl senses gravity by its own cells in inducing gravitropic bending in rice seedlings. In lazy-Kamenoo, although the shoots lost their gravitropic response with the advance of age, sedimentation of amyloplasts itself might not be attributable to the agravitropic growth of the shoots, because, including those of the leaf-sheath bases that had lost their response to gravity, sedimented amyloplasts appeared to be identical to those of normal Kamenoo and of younger seedlings of lazy-Kamenoo whose gravitropism is still apparent.     

Distribution of alcohol dehydrogenase in roots and shoots of rice (Oryza sativa) and Echinochloa seedlings

Abstract Aerobically germinated seedlings of rice and Echinochloa were found to survive when placed in an anaerobic environment for 4 d, whereas pea and maize seedlings did not. Although root and shoot growth were inhibited in rice and Echinochloa under anaerobiosis, growth resumed when the seedlings were returned to aerobic conditions. Alcohol dehydrogenase (ADH) activity increased more, and protein synthesis was greater, in the shoots than in the roots under anaerobic conditions. These results suggest that, in anaerobiosis-tolerant species, ADH activity and protein synthesis in the shoots represents or results from metabolic adaptations to low oxygen. These results are discussed in terms of plant establishment and growth in a low-oxygen environment.     

Cryptic floral determination: stem explants from vegetative tobacco plants have the capacity to regenerate floral shoots

The developmental fates of shoots regenerated in culture and in situ by stem tissues of Nicotiana tabacum cv. Wisconsin 38 from different positions along the main axes of plants at different ages have been characterized. It was expected that explants from vegetative plants would not have the capacity to produce floral shoots. Contrary to the expected result, a small percentage (about 0.2%) of the shoots formed from cultured stem explants taken from young, vegetative plants were floral, i.e., produced a small number of nodes and then a flower. A larger percentage (about 2%) of the shoots formed by explants from the same region of plants which had flowered were floral. The largest percentage (76%) of floral shoots arose from explants taken from the inflorescence. Internode cells which were stimulated to divide and undergo organogenesis in situ after decapitation of the plant also produced few-noded, floral shoots with apical internode tissues producing many such floral shoots and basal internode tissues producing few such floral shoots. These results indicate that the capacity to form a flower is a visible expression of a cryptic developmental state which is quantitatively but not qualitatively controlled in time and space.     

Oxygen supply from shoots to roots relative to the total oxygen consumption in rice roots

A new simplified mathematical model was introduced to assess the rate of oxygen supply to plant roots, and to evaluate separately the longitudinal flux through the aerenchymatous system and the transversal flux from the root medium. The parameters were derived from the experiemntal results with decapitated rice seedlings solution-cultured with aeration. With decreasing oxygen concentration in the root medium, the transversal oxygen flux decreased and the longitudinal flux increased so as to compensate for the decrease of the former, but in some older rice seedlings there was observed a growing insufficiency in oxygen supply to the roots.     

Effects of anoxia on mitochondrial biogenesis in rice shoots: modification of in organello translation characteristics

Shoots of germinating rice (Oryza sativa L.) seedlings are able to grow under anoxia and to withstand long periods of anoxic treatment. Mitochondria were purified from aerobically germinated and anaerobically treated rice shoots by differential and isopycnic centrifugation and were found to consist of two subpopulations. The mitochondrial subpopulation of higher density was used for further characterization. Ultrastructural studies showed anaerobic mitochondria to be significantly different from aerobic mitochondria, with a matrix of lower density and more developed cristae. Aerobic and anaerobic mitochondria also differed in their specific activities for fumarase and succinate dehydrogenase, which were significantly lower after the anoxic treatment. In vivo labeling of seedlings with l-[³⁵S]methionine and subsequent isolation of the mitochondria indicated that anoxia induced a drastic decrease, but not a total inactivation, of the synthesis of mitochondrial proteins. In organello protein synthesis showed that anaerobic mitochondria were able to synthesize most of the polypeptides synthesized by aerobic mitochondria, although only in the presence of exogenous ATP, as would occur under anoxia. Anaerobic mitochondria, but not aerobic mitochondria, could carry out protein synthesis without a functional respiratory chain. Thus, mitochondrial protein synthesis was found to be potentially functional in the rice shoot under anoxia.