Effect of daily photon receipt on the susceptibility of dwarf bean (Phaseolus vulgaris L.) leaves to photoinhibition of photosynthesis

Bean (Phaseolus vulgaris L.) plants were grown at two light periods of 8 and 13 h with a similar photon flux density (PFD) giving a daily photon receipt (DPR) of 17.9 and 38.2 mol · m–2, respectively. Shoot growth and leaf area development were followed at regular intervals and diurnal whole-plant photosynthesis measured. Single mature trifoliate leaves were exposed to photoinhibitory treatments at PFDs of 800 and 1400 mol · m–2 · s–1 and at temperatures of 12 and 20°C. Chlorophyll fluorescence and photon yields were measured at regular intervals throughout each treatment. Plants grown in 13 h had significantly greater leaf areas than those grown in 8 h. There were no differences in maximum rates of photosynthesis, photon yields and only minor but significant differences in F_v/F_m for plants in the two treatments, showing photosynthetic characteristics were dependent on PFD but not DPR. A significant decline in photosynthesis and F_v/F_m occurred over the 13-h but little change in photosynthesis for plants in the 8 h, indicating some feedback inhibition of photosynthesis was occurring. Plants grown in 8 h were consistently more susceptible to photoinhibition of photosynthesis at all treatments than 13-h plants. Nevertheless, photoinhibition was exacerbated by increases in PFD, and by decreases in temperature for leaves from both treatments. However, for plants from the 8-h day, exposing leaves to 12°C and 1400 mol · m–2 · s–1 caused photo-oxidation and severe bleaching but no visible damage on leaves from 13-h-grown plants. Closure of the photosystem II reaction-centre pool was partially correlated with increasing extents of photoinhibition but the relationship was similar for plants from both treatments. There remains no clear explanation for their wide differences in susceptibility to photoinhibition.Abbreviations and Symbols DPR daily photon receipt - F₀ and F_m initial and maximal fluorescence - F_v/F_m fluorescence ratio in dark-treated leaves - F/F_m intrinsic efficiency of PSII during illumination - PFD photon flux density - _i photon yield (incident basis) - _psi quantum yield of PSII electron transport - P_max maximum rate of photosynthesis - q_N non-photochemical quenching coefficient - q_P photochemical quenching coefficient Many thanks to my colleague William Laing who spent a considerable effort in developing the programme to run the photosynthesis apparatus. I am also indebted to one reviewer with whom I corresponded to resolve some issues in the paper. This project was funded by the New Zealand Foundation for Research, Science and Technology.     

Auxins and cytokinins exuded during formation of roots by detached primary leaves and stems of dwarf French bean (Phaseolus vulgaris L.)

Summary Hypocotyls of detached stems standing in culture solution produced adventitious roots sooner than did petioles of detached primary leaves. An auxin, probably indol-3-ylacetic acid, appeared in the solutions before the hypocotyls or petioles produced roots. After attaining a maximum, the amounts of auxin in the solutions decreased as fewer roots were formed. Two cytokinins were found in the culture solutions; one had a similar R_f to zeatin, the other ran more slowly on chromatograms. The amounts of cytokinin in the solutions were associated with root formation. Stems soon died unless their hypocotyls formed roots, but the primary leaves survived without roots forming provided a callus formed on the petiole. Hence adventitious roots, or callus tissues, may have produced cytokinins that replaced those produced by the original roots, found in sap exuded from the stem stumps, and were essential for survival of the stems and leaves.     

Light-stimulated cell expansion in bean (Phaseolus vulgaris L.) leaves

Cell expansion in dicotyledonous leaves is strongly stimulated by bright white light (WL), at least in part as a result of light-induced acidification of the cell walls. It has been proposed that photosynthetic reactions are required for light-stimulated transport processes across plasma membranes of leaf cells, including proton excretion. The involvement of photosynthesis in growth and wall acidification of primary leaves of bean has been tested by inhibiting photosynthesis in two ways: by reducing chlorophyll content of intact plants with tentoxin (TX) and by treating leaf discs with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Exposure to bright WL stimulated growth of intact leaves of TX-treated plants. Discs excised from green as well as from TX-or DCMU-treated leaves also responded by growing faster in WL, as long as exogenous sucrose was supplied to the photosynthetically inhibited tissues. The WL caused acidification of the epidermal surface of intact TX-leaves, but acidification of the incubation medium by mesophyll cells only occurred when photosynthesis was not inhibited. It is concluded that light-stimulated cell enlargement of bean leaves, and the necessary acidification of epidermal cell walls, are mediated by a pigment other than chlorophyll. Light-induced proton excretion by mesophyll cells, on the other hand, may require both a photosynthetic product (or exogenous sugars) and a non-photosynthetic light effect.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1 -dimethylurea - OC osmotic concentration - RL red light - TX tentoxin - WL white light We thank Dr. G.E. Templeton, University of Arkansas, Fayetteville, USA, for initially supplying us with TX, and also Dr. Stephen O. Duke, Southern Weend Science Laboratory, Stoneville, Miss., USA, for suggesting this compound for our experiments. We are grateful to Professor E. Ballio for his generous gift of fusicoccin.     

Light-stimulated cell expansion in bean (Phaseolus vulgaris L.) leaves

The quantity and quality of light required for light-stimulated cell expansion in leaves of Phaseolus vulgaris L. have been determined. Seedlings were grown in dim red light (RL; 4 micromoles photons m-2 s-1) until cell division in the primary leaves was completed, then excised discs were incubated in 10 mM sucrose plus 10 mM KCl in a variety of light treatments. The growth response of discs exposed to continuous white light (WL) for 16 h was saturated at 100 micromoles m-2 s-1, and did not show reciprocity. Extensive, but not continuous, illumination was needed for maximal growth. The wavelength dependence of disc expansion was determined from fluence-response curves obtained from 380 to 730 nm provided by the Okazaki Large Spectrograph. Blue (BL; 460 nm) and red light (RL; 660 nm) were most effective in promoting leaf cell growth, both in photosynthetically active and inhibited leaf discs. Far-red light (FR; 730 nm) reduced the effectiveness of RL, but not BL, indicating that phytochrome and a separate blue-light receptor mediate expansion of leaf cells.     

Effect of Calcium on Sodium Salinization of Beans (Phaseolus vulgaris L.)

The efficiency of calcium in enhancing the tolerance of beans(Phaseolus vulgaris L.) to sodium salinization was studied inpot experiments in both cool and hot seasons. In the cool seasonincreased yields of dry matter, roots, nodules and pods werepositively correlated with increased Ca application and negativelycorrelated with the Na contents of irrigation water and planttissue. The Na levels both in roots and tops declined significantlyas increased amounts of calcium were added. Ca in the rangeof 2.0 to 8.0 mmol/1 caused competitive inhibition of Na uptakeand Na translocation. At Ca levels between 0 to 2.0 mM onlyNa translocation to tops was markedly inhibited. In warm seasonsCa had no beneficial effects on bean yields at any level ofNa. On the contrary, high rates of Ca application resulted ina higher death rate.     

Photoinhibition of photosynthesis in dwarf bean (Phaseolus vulgaris L.) leaves: effect of sink-limitations induced by changes in daily photon receipt

Bean (Phaseolus vulgaris L. cv. Long John) plants were grown with photoperiods of 6 and 16 h at constant photon flux density (PFD), giving a daily photon receipt (DPR) of 17 and 48 mol · m⁻² respectively. Vegetative growth was determined at regular intervals and diurnal whole-plant photosynthesis measured. Intact trifoliate leaves were exposed to photoinhibitory treatments at PFDs of 800 and 1400 μmol · m⁻² · s⁻¹ at temperatures of 14 and 20 °C, both in the absence and presence of the inhibitors chloramphenicol and dithiothreitol. Fluorescence and photon yields were determined at regular intervals throughout each treatment. Plants grown with photoperiods of 6 h had significantly lower growth rates than those grown with 16-h photoperiod but no difference in net photosynthetic rates or photon yields were found. Carbohydrate analyses confirmed short-day plants were strongly sink-limited. Long-day plants were slightly sink-limited, with a high proportion of starch in the leaves and reduced photosynthesis between 13 and 16 h. Plants grown in low DPR were more susceptible to photoinhibition, from sustained closure of some photosystem II reaction centres, than plants grown in high DPR. Capacity for thermal dissipation appeared dependent on PFD while photochemical capacity was more dependent on DPR. Received: 6 June 1997 / Accepted: 17 September 1997     

Plastid development in primary leaves of Phaseolus vulgaris

Summary The development of increased activities of ribulosediphosphate carboxylase (EC 4.1.1.39) and of phosphoribulokinase (EC 2.7.1.19) in greening bean leaves was completely inhibited by D-threo chloramphenicol but unaffected by L-threo chloramphenicol. This indicates that these enzymes are synthesized by the ribosomes of the developing plastids. A different mechanism appears to be responsible for the development of activity of NADP-dependent triosephosphate dehydrogenase (EC 1.2.1.13) where the D-threo isomer gave 45% inhibition and the L-threo isomer gave 18% inhibition. Thus both specific (D-threo isomer) and unspecific (both isomers) inhibition occurred. It is suggested that the development of NADP-dependent triosephosphate dehydrogenase activity may result from the allosteric activation, in the plastids, of the NAD-dependent enzyme (Müller et al., 1969) which has been synthesized by cytoplasmic ribosomes. Neither isomer inhibited the development of five other enzymes of the photosynthetic carbon cycle namely ribosephosphate isomerase (EC 5.3.1.6), phosphoglycerate kinase (EC 2.7.2.3), triosephosphate isomerase (EC 5.3.1.1), tructosediphosphate aldolase (EC 4.1.2.13) and transketolase (EC 2.2.1.1), but there was a significant stimulation of the activity of transketolase by D-threo chloramphenicol.     

Effect of silicon on manganese tolerance of bean plants (Phaseolus vulgaris L.)

Summary The effect of silicon on manganese tolerance of bean plants (Phaseolus vulgaris L. var. ‘Red Kidney’) grown in water culture was studied at different levels of manganese supply. Without silicon, growth depression and toxicity symptoms occurred already at 5 × 10⁻⁴ mM Mn in the nutrient solution. After addition of Aerosil (0.75 ppm Si), the plants tolerated 5 × 10⁻³ mM Mn and, at a higher silicon supply of 40 ppm, as much as 10⁻² mM Mn in the nutrient solution without any growth depression. This increase in manganese tolerance was not caused by a depressing effect of silicon on uptake or translocation of manganese but rather by an increase in the manganese tolerance of the leaf tissue. In absence of silicon, 100 ppm Mn was already toxic for the leaf tissue, whereas with a supply of 40 ppm Si, this ‘critical level’ in the leaves was increased to more than 1000 ppm Mn. At lower manganese levels in the leaf tissue, a molar ratio Si/Mn of 6 within the tissue was sufficient to prevent manganese toxicity. Above 1000 ppm Mn, however, even a much wider Si/Mn ratio (> 20) could not prevent growth depression by manganese toxicity. With⁵⁴Mn and autoradiographic studies, it could be demonstrated that, in absence of silicon, even at optimal manganese supply (10⁻⁴ mM), the distribution of manganese within the leaf blades was inhomogeneous and characterized by spot-like accumulations. In presence of silicon, however, the manganese distribution was homogeneous in the lower concentration range of manganese and still fairly homogeneous in the high concentration range. This effect of silicon on manganese distribution on the tissue level was also reflected on the cellular level. In the presence of silicon, a higher proportion of the leaf manganese could be found in the press sap,i.e., had been transported into the vacuoles, than in the absence of silicon. The increase in manganese tolerance of bean leaves by silicon therefore seems to be primarily caused by the prevention of local manganese accumulation within the leaf tissue which leads to local disorders of the metabolism and, correspondingly, growth depression.     

Effect of Glyphosate on Intact Bean Plants (Phaseolus vulgaris L.) and Isolated Cells

Whole bean (var. “Eastern Butterwax”) plants and isolated cells were used to investigate possible mechanisms of action of glyphosate [N-(phosphonomethyl)glycine]. Results showed that glyphosate was quickly absorbed by the whole plant but not by individual cells and that it caused a rapid reduction in leaf dry matter accumulation, leaf expansion, leaf angle, and stomatal aperture without affecting the water status of the plant. Glyphosate also caused a rapid reduction in cellular uptake of ⁸⁶Rb and ³²P which preceded its detrimental effects on photosynthesis, RNA and protein synthesis, and respiration of isolated cells. This reduction in ion absorption was not due to a loss of membrane integrity, decrease in energy supply or chelation of ions. It was concluded that glyphosate was directly inhibiting the ion absorption process of bean leaf cells.     

Effects of temperature on infection of French bean leaves (Phaseolus vulgaris L.) by lucerne mosaic virus

The effect of temperature on the number of lesions and the time of their appearance was studied by inoculating French bean leaves (Phaseolus vulgaris L. cv. Perli?ka) with lucerne mosaic virus either 24 or 48 h before or, 24 or 48 h after they were exposed to various temperatures. The temperatures tested were 23, 25, 27, 30, 33 and 36° C. Before and after such exposures the plants were kept in a constant temperature of 25° C. By increasing the temperature before inoculation the number of lesions increased in comparison with the control. The optimal temperature for the maximum number of lesions is between 27° and 30° C. There is no significant difference between those experiments when the exposure time was 24 h or 48 h before inoculation. The same temperatures applied for 24 or 48 h after inoculation have a decreasing effect upon the number of lesions formed by LMV on French bean leaves. The decrease is 30 to 75%. In this case the first necrotic local lesions appeared 42 h after inoculation when exposed to higher temperatures above 27° C for 24 h, and 60 h after inoculation when exposed to these temperatures for 48 h. The shape of lesions varied a little in both cases as the pictures show.     

Role of acid efflux during growth promotion of primary leaves of Phaseolus vulgaris L. by hormones and light

The white-light-(WL) induced enlargement of dicotyledonous leaf cells is known to occur via an acid-growth mechanism; i.e., WL causes leaf cells to excrete protons which lead to an increase in wall extensibility and thus cell enlargement. Gibberellic acid (GA₃) and N⁶-benzyladenine (BA) also induce leaf cell enlargement. To see if they also act via acid-induced cell wall loosening, a comparison has been made of WL-, GA₃-and BA-induced growth of strips, taken from primary leaves of bean (Phaseolus vulgaris L.) plants raised in continuous red light for 10 d. White light, GA₃ and BA all increased wall extensibility as measured by the Instron technique, and this change preceded the increase in growth rate. However, whereas WL induced significant proton excretion, neither GA₃ nor BA caused any acidification of the apoplast. Furthermore, neutral buffers, which effectively inhibited the growth induced by WL, were without effect on growth promoted by either GA₃ or BA. These results indicate that while WL, GA₃ and BA all initiate growth in bean leaves by altering cell-wall properties, GA₃ and BA do so through some wall loosening mechanism other than wall acidification. Neither gibberellin nor cytokinin is likely to play a major role in light-induced cell enlargement of dicotyledonous leaves.Abbreviations BA N^o-benzyladenine - FC fusicoccin - GA₃ gibberellic acid - RL red light - SK medium 10 mM sucrose+10mM KCl - WL white light     

Macronutrient content in leaves of bean plants (Phaseolus vulgaris,L.) grown with differents rates of N/S as fertilizers

Summary The effect of increasing rates of nitrogen (N) and sulphur (S) as fertilizers on the yield, leaf area and N, P, S, Ca, Mg, NO₃ ⁻ and SO₄ ⁼ content in leaves of bean (Phaseolus vulgaris, L.) were studied in a hydroponic culture experiment under greenhouse conditions. Bean plants responded significantly to all treatments with differents N/S ratios. When plants grew with high N/S ratios, the leaf content of N, Ca and NO₃ ⁻ increased while the content of K, P and SO₄ ⁼ decreased. However, optimal yield and leaf area were not obtained. Optimal leaf and fruit dry matter was obtained at N/S ratio value of 1.41. When lower N/S rates were used, optimal leaf and fruit dry matter was only observed when the leaf N/S ratio was between 15 and 16. At high sulphate levels in the nutrient solution there is no interaction with nitrate which is easily observed, resulting in an increase in yield. An interaction between nitrate and sulphate in the nutrient solution was found at a N/S ratio of 0.81 which produced in leaves a synergic effect between P-K, an antagonistic effect between N-P and N-K and a lower yield. This research was supported by Fundacion ‘Ramon Areces’.     

Effect of Non-auxin Chemicals on Translocation of Auxins in Cuttings of Phaseolus vulgaris (L.)

Indole, -naphthol, pyrogallol, coumarin, and salicylic acidinteracted with the auxins, IAA (indol-3yl-acetic acid), NAA(naphth-lyl-acetic acid), and 2, 4-D (2, 4-dichlorophenoxyaceticacid), supplied to the basal ends of cuttings of Phaseolus vulgaris(L.), giving synergistic or antagonistic effects in root formation.Antagonism in rooting was always associated with increased accumulationof radiocarbon from carboxyl-¹⁴C-labelled auxins in the topsof the cuttings. Distribution of auxin over a greater lengthof the cutting was accompanied by a reduction in root formation.The chemicals which synergized auxin-induced root formationdid not promote accumulation of radiocarbon of the exogenouslyapplied labelled auxins in the upper parts of the cuttings.     

The nature of heterogeneity in the stomatal behaviour of Phaseolus vulgaris L. primary leaves

The aim of this research was to investigate the nature of heterogeneity in stomatal conductance and, in particular, to determine whether the characteristic 'patchy' pattern of water infiltration is reflected in measurements on individual stomata. Silicone rubber replicas were made of primary leaves of glasshouse-grown Phaseolus vulgaris L. plants, and the leaves were then infiltrated with water at controlled sub-atmospheric gas pressures according to their estimated or measured stomatal conductance. Seven leaves examined in detail all showed patchy infiltration, and the mean sire of infiltrated areas was negatively correlated with the prevailing stomatal conductance. In four of the leaves, a one millimetre wide transect across the leaf was selected for further detailed study. Measurements of mean peristomatal groove distance (PGD) and stomatal frequency were made along the transect and related to the state of infiltration. Analysis of variance indicated that, in all four cases, variation in PGD among patches was highly significant, but there was no significant difference between patches of different infiltration categories. Thus, local (patch-level) variation in stomatal aperture appeared to bear no relation to the infiltration status of the patches. The dominant source of stomatal variability was between individual pores in the same locality, which accounted for 82% or more of the total variability. Taking into account variation in stomatal frequency, correlations between predicted stomatal conductance and the extent of infiltration were significant in only one out of the seven leaves studied. Possible reasons for these results are discussed. It is suggested that the infiltration method misrepresents the underlying state of the stomata as being either open or closed, when there is little evidence for this from measurements of stomatal dimensions. For these unstressed plants under relatively stable conditions, it is concluded that the 'unit of variability' in stomatal heterogeneity may rest at the individual pore ('micro') scale, rather than at the areolar patch ('macro') scale, or above.