Effects of Shading the First Leaf on Growth of Barley Plants: II. Effects on Photosynthesis

The contributions made by photosynthesis in the first leaf toseedling growth have been examined by a variety of methods includinginfra-red gas analysis and the use of ¹⁴CO₂. The first leafis fully expanded by day 8 and maximal rates of photosynthesisare achieved about I day later. Up to day 8 growth of the seedlingsresults from the redistribution of seed reserves and once theseare exhausted growth is dependent upon the first leaf, beingreduced to very low levels if this is shaded. The second leafwhich begins to expand rapidly after day 10 is contributingto growth by day 14, and the contribution from the first leafbegins to decline after day 12. Apart from greatly reducing photosynthesis in treated leaves,shade also affects the development of photosynthetic capacity.When applied for 2 days or more from day 6, shade reduces thepeak level of carbon fixation achieved on days 9 and 10 by upto 35 per cent. It is shown that development of the first leafin terms of increased dry weight and photosynthetic capacity,is dependent on photosynthesis in the developing leaf itself.The mechanisms by which shading affects development are discussed.     

Effects of Shading the First Leaf of Barley Plants on Growth and Carbon Nutrition of the Stem Apex

Effects of shading the first leaf on development of the apicalregion were investigated by examining the growth of leaf primordiaand the apical dome in the early seedling stages. Shade treatment affects the size of the dome; it was shown thatvalues for height, width, and volume of the dome of 12-day controlplants were always higher than for shaded plants. Primordialgrowth, in terms of length and dry weight, was reduced by shadeand growth in dry weight of the second, third, and fourth leaveswas shown to be dependent on photosynthetic production by thefirst leaf. Incorporation of ¹⁴C in the apical region was detected by autoradiographyon day 6 and increased with age. Transfer of assimilated carbonfrom the first leaf to the apex occurred during the first 3h after exposure to ¹⁴CO₂. On a unit dry-weight basis it isshown that the third and fourth leaves and apex incorporatedproportionately more labelled carbon than the larger older organssuch as the, second leaf. Shade treatment reduced incorporationinto the apical region and this is associated with the failureof the apex to grow over the period up to day 15. Evidence isprovided to show that in control plants the second leaf suppliescarbon to the apex from about day 12. The crucial importanceof the contribution of the first leaf to plant development isdiscussed.     

The Effects of Nitrate Supply and Grain Reserves on Fraction I Protein Level in the First Leaf of Barley

The timing and rate of nitrate application to barley seedlingsgrown under control and shade conditions can appreciably affectthe maximum amount of Fraction I protein attained in the firstleaf lamina. In unshaded seedlings early application resultsin a higher maximum amount of Fraction I protein per lamina,but not per unit lamina fresh weight. Late application of nitratehowever delays the age at which Fraction I protein reaches amaximum both in absolute terms and as a proportion of totalsoluble protein. For both control and shade-grown material earlyand higher rates of nitrate supply increase the maximum amountof soluble protein in the leaf but not the proportion representedby Fraction I protein. Lower rates of nitrate application havemuch less effect on first-leaf protein synthesis when applicationis given late. This is thought to be due to competition fromthe rapidly developing second leaf. Studies on the soluble protein content of shaded first-leaflaminae have shown that although grain size affects the maximumamount of Fraction I protein attained it does not alter theage at which this is attained; nor is the proportion of thetotal soluble protein accounted for by Fraction I protein affectedby grain size or grain nitrogen content. A model is proposed to explain the contribution made by grainreserves and exogenous carbon and nitrogen supply to the developmentof the soluble protein content of the first leaf.     

Effects of Growth Regulators on Ribonucleic Acid Metabolism of Barley Leaf Segments

Illumination or gibberellic acid treatment of etiolated barley leaf segments stimulates unrolling and results in an increased level of RNA. In contrast, segments treated with abscisic acid do not unroll and have a lower content of RNA. Gibberellic acid treatment enhanced the capacity of segments to incorporate radioactivity from ³²P-orthophosphate into all the RNA components detected by gel electrophoresis; abscisic acid greatly restricted the incorporation of precursors into all the RNA fractions. In conjunction with a changed capacity for RNA synthesis it was observed that abscisic acid-treated segments had a lowered soluble DNA-dependent RNA polymerase level in comparison to gibberellic acid-treated or illuminated segments. However, the influence of growth regulators on RNA polymerase content of the segments was associated with general effects on protein level rather than a specific effect on the synthesis of polymerase enzyme.     

The Effects of Grain Nitrogen and Applied Nitrate on Growth, Photosynthesis and Protein Content of the First Leaf of Barley Cultivars

Five cultivars of barley with widely differing grain nitrogencontents were compared. In the absence of exogenous nitratesupply plants grown from high nitrogen grain showed a more rapidleaf emergence, greater leaf size, especially of the first leaf,higher photosynthetic rate and greater total souble proteinand Fraction 1 protein content of the first leaf, than plantsgrown from low nitrogen grain. However, early supply of nitrateto plants grown from low nitrogen grain enabled these to performas well as those from grain with a high nitrogen content. Regressionanalysis showed that Fraction 1 content of the first leaf isclosely correlated with grain nitrogen which exerts a progressivelygreater effect on content of this protein as application ofexogenous nitrate is delayed. The more rapid photosyntheticrate of plants grown with high nitrogen, and the consequentgreater rate of dry matter accumulation, is attributable mainlyto effects of nitrogen availability on leaf area and much lessto effects on leaf protein.     

The Effect of Salinity on Growth of Phaseolus vulgaris L.: I. Anatomical Changes in the First Trifoliate Leaf

When plants of Phaseolus vulgaris were grown in culture solutioncontaining 48 m mol l^–1 sodium chloride, the first trifoliateleaves were always smaller in area than those of control plants.The leaves of the salt-treated plants however could become thicker.This increase in thickness was brought about by the increasein the thickness of the spongy parenchyma layer. The palisadeparenchyma layer was always thinner than that in the controlleaves. While these latter leaves expanded predominantly bycell division, this only held for the early stages of expansionof the leaves of salt-treated plants. In this case cell divisionceased when the leaves were about half their maximal size andfurther increase in area was brought about by an increase involume of the spongy parenchyma cells.     

Growth and Photosynthesis in the First Leaf of Barley The Effect of Time of Application of Nitrogen

Using Proctor barley grown in sand under controlled-environmentconditions it was shown that when application of nitrogen, asnitrate, was delayed beyond day 4, at which time the first leafwas beginning to unfold, absolute and relative growth-ratesof seedlings were reduced so that the young plants were significantlysmaller. Delay in nitrate application led to reduction in length,breadth, area, and dry weight of the first leaf, and also toa lower photosynthetic activity on day 8, as measured by infra-redgas analysis. Measurement of the uptake of ¹⁴CO² by first leaves showed thatapplication of nitrate on days 2 or 4 led to high rates of fixationof carbon over the period days 8–12, whereas applicationon days 6 or 8 led to a substantially lower maximum rate offixation which was maintained for a shorter period. When nitratewas applied on day 8 total fixation of carbon over the perioddays 7–14 was only 60 per cent of that for leaves on plantsfor which nitrate was supplied on day 2. When amounts of carbon fixed were compared on a leaf dry-weightbasis, maximum values were found to be similar for all treatments,suggesting that the differences in fixation per leaf resultmainly from the effect of treatment on leaf area. For all treatmentsit was confirmed that a decline in photosynthetic activity occurredby day 14. This was not correlated with photosynthetic activityin the second leaf, nor with emergence of the third leaf. Analysis of different parts of the lamina of the first leafshowed all to be affected by the timing of the supply, bothin growth and in photosynthetic activity. Leaf dry weight didnot increase after day 8 for any treatment, yet when nitratewas applied on day 8 plants showed a fourfold increase in photosyntheticrate. The significance of this in relation to carboxylationand other resistances in photosynthesis is discussed.     

Chloroplast Protein Synthesis During Barley Leaf Growth and Senescence: Effect of Leaf Excision

Chloroplast protein synthesis was measured during the expansion,maturity and senescence of the oldest leaf of barley, Hordeumvulgare L., var. Hassan. A maximum rate of protein synthesisoccurred near the end of the expansion stage 9 d after sowing.Protein synthesis increased again at the beginning of senescenceand reached a new maximum at day 14 after sowing. Detachmentand incubation of leaves in the dark stimulated chioroplastprotein synthesis by fully expanded or by senescent leaves butnot by expanding leaves. If the detached leaves were kept inthe light, chloroplast protein synthesis was stimulated in fullyexpanded but not in senescent leaves. Short treatments (18 h)of leaf segments with growth substances in either light or indarkness, significantly changed the rate of protein synthesisshown by chloroplasts. The relationship between chloroplastprotein synthesis and leaf senescence is discussed. Key words: Hormones, light, maturity     

遮荫处理对梅叶冬青叶片形态、光合特性和生长的影响

为了解遮荫环境对梅叶冬青(Ilex asprella)生长和光合特性的影响,采用遮荫网的方法模拟85%、56%和全光照等3种光照环境,研究了遮荫对其生长、光合参数以及生物量等的影响。结果表明,经一年遮荫处理后,梅叶冬青的叶绿素a、b和叶绿素总量都随着遮荫强度的增加而显著增高,胡萝卜素含量则显著降低。与对照相比,56%遮荫处理显著提高梅叶冬青的最大净光合速率和光饱和点,分别提高了17.6%和25.2%,但是85%遮阴处理则显著降低最大净光合速率和光饱和点,分别降低了18.2%和24.1%,两种遮荫处理均显著降低了光补偿点。叶长、叶宽、比叶面积、单片叶面积和叶片含水量均随着遮荫强度的增加而显著增加,而叶片厚度则显著减小。遮荫处理明显抑制整株生物量增长,减小根冠比,但是株高、冠幅和径向生长随遮荫处理时间不同而有所变异。因此,梅叶冬青有耐荫偏阳的特性,在林下种植时需及时调控乔冠层的透光率,一般应大于44%。     

The Effects of Cotyledon Excision on Growth and Leaf Senescence in Soya-bean Plants

One effect of the removal of cotyledons of soya-beans 24 h afterimbibition was to reduce subsequent growth, especially in thefirst 10 weeks after planting. The longevity of treated plantswas increased by 30 days and the onset of leaf senescence delayed,as judged by the time-course of leaf chlorophyll and solubleprotein content, and also by the time-course of net photosynthesisand respiration rates. These effects are similar to those reportedto result from partial defoliation of more mature plants.     

The Effects of Shade Treatment and Light Intensity on Rihulose-1,5-Diphosphate Carboxylase Activity and Fraction I Protein Level in the First Leaf of Barley

It has been confirmed that shading leaves from day 5 onwardslowers the rate of CO₂ fixation when they are placed in saturatingirradiances. The reduction due to shade treatment is about 46per cent and a similar reduction in maximum chlorophyll contentof the leaf follows shading. Maximum amounts of total solubleprotein and of Fraction I protein are less in shaded leavesthan in control leaves and prolonged treatment leads to a declinein leaf protein content. The relative amounts of different proteinare also affected by treatment; in control leaves Fraction Iprotein accounts for about 45 per cent of the total but in shadedleaves the value is about 30 per cent. Increases and decreasesin leaf protein amount, with concomitant changes in the ratioof Fraction I to total protein can be brought about by removingshades and re-applying them. Such changes can be induced evenin fully expanded leaves in which net protein synthesis is notusually found. Maximal amounts of leaf protein are found in irradiances of60 W m^–2 or more, with lower values at lower light intensities.Where the first leaf is held in a stream of CO₂-free air a lowerlevel of protein is found. This, and the ratio of Fraction Ito total protein, are similar to values for shaded leaves, andsuggest the involvement of photosynthetic carbon fixation indetermining leaf protein amount. A 1:1 linear correlation between amount of Fraction I proteinand RuDP carboxylase activity is shown but the rate of CO₂ incorporationby leaf extracts is 2–3 times greater than that of theintact leaf. The significance of this and the effect of irradianceon leaf protein amount are discussed.     

Effects of CO2 Enrichment on Four Poplar Clones. I. Growth and Leaf Anatomy

The poplar clones Columbia River, Beaupre, Robusta and Raspaljehave been investigated under the present (350 µmol mol^–1)and double the present (700 µmol mol^–1) atmosphericCO₂ concentration. Cuttings were planted in pots and were grownin open-top chambers inside a glasshouse for 92 d. The number of leaves, total length of stem, total leaf area,overall growth rate, total leaf, stem and root d. wt respondedpositively to increased CO₂ but the leaf size and biomass allocationshowed no change with CO₂ enrichment. Beaupre and Robusta showeda larger growth response than either Columbia River or Raspalje. The effects of CO₂ enrichment were restricted to the early phaseof growth at the beginning of the growth season. Leaf cell numbers in all the clones were not affected by CO₂enrichment. Leaf thickness was affected; this was mainly theresult of larger mesophyll cells and more extensive intercellularspaces. Poplar clones, CO₂ enrichment, growth, leaf anatomy, leaf cell number     

Effect of Salicylic Acid on Leaf Anatomy and Chloroplast Ultrastructure of Barley Plants

Light and electron microscopy were used to relate histological and ultrastructural differences of barley leaves treated with different concentrations of salicylic acid (SA, 100 µM-1 mM). Light microscopy revealed that the thickness of all leaf tissue components decreased in SA-treated plants. The effect was most pronounced on the width of the adaxial epidermis and on the size of the bulliform cells. The chloroplast ultrastructure was also affected by SA treatment. Swelling of grana thylakoids in various degrees, coagulation of the stroma, and increase in chloroplast volume were observed. 1 mM SA caused a vast destruction of the whole plastid structure.     

Changes in Properties of Barley Leaf Mitochondria Isolated from NaCl-Treated Plants

Treatment of barley (Hordeum vulgare) seedlings with 400 millimolar NaCl for 3 days resulted in a reduction in plant growth and an increase in the leaf content in ions (K⁺ + Na⁺) and proline. Purified mitochondria were successfully isolated from barley leaves. Good oxidative and phosphorylative properties were observed with malate as substrate. Malate-dependent electron transport was found to be only partly inhibited by cyanide, the remaining oxygen uptake being SHAM sensitive. The properties of mitochondria from NaCl-treated barley were modified. The efficiency of phosphorylation was diminished with only a slight decrease in the oxidation rates. In both isolated mitochondria and whole leaf tissue of treated plants, the lower respiration rate was due to a lower cytochrome pathway activity. In mitochondria, the activity of the alternative pathway was not modified by salt treatment, whereas this activity was increased in whole leaf tissue. The possible participation of the alternative pathway in response to salt stress will be discussed.     

Changes in the Leaf Polypeptide Patterns of Barley Plants Exposed to Soil Flooding

Exposure of barley plants (Hordeum vulgare L.) to soil flooding for 72 – 120 h led to decrease in the content of the both subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase. The effect was more pronounced on the small subunit. Further, the changes in protein pattern were observed, mainly proteins with molecular masses 30 – 85 kD were down-regulated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of lodine in Various Formulations on the Growth of Barley and Pea Plants in Nutrient Solution Culture

The forms of iodine added to cultures of barley were potassiumiodide, potassium iodate, potassium periodate, and iodoaceticacid at iodine concentrations of 1.0 ppm and 10.0 ppm. Withpea, only iodide and iodate at 1.0 ppm iodine concentrationwere used. For both species, comparisons were made with culturesto which no iodine was added. In barley, growth was increased by 1.0 ppm iodine, the relativeeffectiveness of the different formulations being in the order:iodoacetic acid > iodide > iodate > periodate. With10.0 ppm, iodide and iodoacetic acid treatments gave reducedgrowth, iodate was without effect, and periodate enhanced growth. In pea, 1.0 ppm iodine was inhibitory, iodide being more toxicthan iodate. Analysis of dry matter showed iodine content according to treatmentto be in the order: iodide > iodoacetic acid > iodate> periodate     

不同光照梯度的遮荫处理对绒毛番龙眼幼苗生长的影响

在不同光照梯度,即100%自然全光照(natural sunlight,NS)、37.3%NS、15.5%NS、4.2%NS、1.6%NS和0.6%NS的人工遮荫条件下,研究了西双版纳季节雨林冠层树种绒毛番龙眼(Pometia tomentosa)幼苗的早期生长和定居后的生长特点。结果表明,光照是影响幼苗生长的重要环境因子。生长早期的幼苗基径和复叶数随遮荫程度的增加而降低;主根长、根冠比、总干重和单株叶面积均以37.3%NS处理最大;比叶面积随遮荫程度的增加而增大,而相对生长率则降低;幼苗株高在0.6%NS下增长最快,表明种子中贮藏的营养物质对幼苗的早期生长可能具有重要作用。37.3%NS处理对定居后绒毛番龙眼幼苗的生长最有利,幼苗的株高、基径、复叶数、叶轴长、复叶最多小叶数、单株叶面积、相对生长率和净同化率均在37.3%NS处理下获得最大增长;幼苗总干重随光照强度的减弱而降低;比叶面积在15.5%NS处理时最大。幼苗比叶面积和根冠比在生长过程中的波动可能是光照和土壤水分共同作用的结果。