Effect of Moisture Supply upon Translocation and Storage of 14 C in Sugarcane

The effects of salinity on corn plants (Zea mays L.) are influenced by the concentration of nutrient orthophosphate. Salinity (-2 bars each of NaCI and CaCI2) was more injurious in combination with a high concentration of orthophosphate (2 mM) (that gave optimum yields in the absence of salinity) than it was with a lower concentration (0.1 mM). With 2 mm orthophosphate, salinity seemed to damage the plant mechanisms that normally regulate the internal concentration of orthophosphate resulting in excessive accumulation and P toxicity. On the other hand, with 0.1 mM orthophosphate, salinity decreased orthophosphate concentration in mature leaves. This effect was paralleled by decreases in the concentration of adenosine 5'-triphosphate and in the energy charge of the adenylate system, indicating an orthophosphate deficit. Even so, plants survived salinity better under these conditions than in the presence of 2 mM orthophosphate. The data indicated that salinity affected the phosphorylated state of the adenine nucleotides only indirectly through its effect on the concentration of orthophosphate in the cells. Salinity, especially in the presence of 2 mM orthophosphate, resulted in an increase in the concentrations of sugar phosphates in mature photosynthesizing leaves, suggesting that translocation rather than photosynthesis was a limiting process. Decreased translocation could be a secondary effect of decreased growth. However, a decreased translocation rate could cause decreased growth by limiting the supply of essential metabolites reaching growing tissues.The recent salinity-fertility studies of Bernstein et al. (7) showed a marked interactive effect of salinity and nutrient Pi on corn plants. Salinity was more deleterious in combination with a high concentration of Pi (2 mM) than with a low concentration (0.05 mM). There occurred a greater reduction in yield and a characteristic leaf injury. The injury seemed to be a result of excessive accumulation of P; other ions did not accumulate sufficiently to account for it. Also, the injury signs were similar to those caused by P toxicity in wheat (8) and barley ( 15). These observations suggested that salinity affected the uptake and utilization of Pi by the plants. Considering the central role of P in cell metabolism, evidence of salt-induced changes in P metabolism might also provide insight regarding the mechanism of salt injury to plants. The work reported here was concerned with the effects of salinity in combination with low and high concentrations of nutrient Pi on the concentrations of Pi and of Pesters2 in mature photosynthesizing corn leaves. Preliminary ' This paper is dedicated to a fellow plant physiologist and friend.Leon Bernstein.2 Abbreviations: F6P: fructose 6-phosphate; FDP: fructose 1 6-diwork showed that salinity, like extremes in P nutrition (9), affected the concentrations of these compounds much more than it did the concentrations of lipid P and nucleic acid P. MATERIALS AND METHODS Plant Culture. Corn plants (Zea mays L. T-strain Golden...

Section: Discussionmentioning

confidence: 99%

Interactive Effects of Salinity and Phosphorus Nutrition of the Concentrations of Phosphate and Phosphate Esters in Mature Photosynthesizing Corn Leaves

Nieman¹,

Clark²

1976

“…To study the third possibility, an experiment was conducted with detached blades. Although all the -N blades were much yellower than the controls, there was no difference in translocation either at 2000 ft-c or in the dark (Table IV) (9). in the stalk.…”

mentioning

confidence: 99%

Effect of Nitrogen Deficiency upon Translocation of ¹⁴C in Sugarcane

Hartt¹

1970

Self Cite

Withholding nitrogen decreased the percentages of nitrogen and chlorophyll in the blades; reduced the total fixation of radioactive carbon dioxide at 15, 37, and 178 seconds; and changed the relative composition of fixation products. Translocation of radioactive photosynthate from the fed part down the attached blade and into the stalk was less in the plants deprived of nitrogen than in the control plants supplied with nitrogen. Both the percentage of total activity translocated and the velocity of transport were decreased by nitrogen deficiency. During a translocation period of 90 minutes the minus nitrogen blade retained more '4C-sucrose than the control in the fed part and the blade below the fed part, but it sent less '4C-sucrose to the sheath of the fed leaf. Thus translocation decreased with nitrogen deficiency not for lack of sucrose but for some other reason. Although withholding nitrogen decreased translocation of labeled carbon in and from attached blades, there was no effect upon transport in detached blades. The effect of nitrogen deficiency upon translocation may be indirect and secondary to the effect upon growth of the plant as a whole.Factors affecting translocation of 'IC in sugarcane include supply of K, N, and P (8,10,11 and whether the N is supplied as NO3-or NH4+ (2,5). N nutrition may also affect the composition of the translocate (16).The purpose of this paper is to report the effect of N deficiency upon translocation in sugarcane plants which was Equal doses of 14CO2 were supplied to 20-cm lengths of blade of intact plants outdoors where grown, by the use of the chamber described previously (8). Translocation was terminated by cutting the plant into the required parts. Samples were prepared and their radioactivity was determined by methods already presented in detail (13). Briefly, at harvest the plants were subdivided, weighed, and sampled. Dried, milled samples were counted at infinite thickness. Samples of extracts were counted at infinite thinness. Samples for sugar analyses were boiled and extracted with ethanol. Sugars were analyzed by the method described by Tanimoto and Burr (18) and chromatographed by the methods given previously (13). Chromatograms were counted on the paper.Results counted at infinite thickness are expressed as relative specific activity (the net cpm at infinite thickness), relative total counts (the relative specific activity times the total dry weight in milligrams), and percentage of relative total counts in the plant or detached blade (obtained by adding the relative total counts of each part). Results counted at infinite thinness are expressed as total counts.Methods for Photosynthesis Test. The early and later stages in photosynthesis (15, 37, and 178 sec) were studied in one experiment. Three sections of blade each 7.5 cm long, including midrib and lamina, were cut from the central part of blade 42 of a control plant and also of a plant deprived of N. Alternate sections of + and -N blades stood in a trough of water at the base of a wire rack whi...

“…Inhibition of assimilate translocation by water stress has been observed in a number of plant species (6,7,11,13). Wardlaw (19,20) Disagreement exists as to the relative sensitivity of photosynthesis and translocation to water stress.…”

mentioning

confidence: 99%

Relative Sensitivity of Photosynthetic Assimilation and Translocation of ¹⁴Carbon to Water Stress

Sung¹,

Krieg²

1979

The relationship between photosynthesis and translocation rate changes as affected by water stress intensity and stage of plant development was evaluated in cotton and sorghum, representing a C3 and a C4 photosynthetic type, respectively. Photosynthetic rates were reduced as midday leaf water potentials declined from -14 to -27 bars in both species. Sorghum maintained higher photosynthesis and translocation rates compared to cotton at comparable leaf water potentials; however, the rate of change per bar decline in water potential was greater in sorghum than in cotton. Photosynthetic rates were reduced with increasing water stress prior to any significant change in translocation rates suggesting that photosynthesis is the more sensitive of the two processes. Severe water stress, corresponding to leaf water potentials of -27 bars, did not completely inhibit either photosynthesis or translocation.Photosynthetic rate reductions due to increasing water stress have been observed in a variety of plant species. Stomatal effects are usually considered to be the first and major limitation to CO2 fixation, although inhibitions at the chloroplast level have been proposed (5, 10). Under semiarid field conditions, stomatal closure is not evident in fully illuminated cotton leaves even at Iw2 approaching -30 bars; however, photosynthesis is severely reduced (1, 2). In this same environment, stomatal regulation is observed only prior to flowering in sorghum's response to increasing water stress (1). Photosynthetic rates of individual leaves of sorghum are significantly reduced prior to any measurable increase in stomatal resistance. After the leaf has attained maximum size no evidence of stomatal closure exists in response to increasing water stress; however, photosynthetic rates are severely affected (12, and unpublished data of Krieg).Leaf photosynthesis may be affected by accumulation of photosynthate due to effects on translocation or utilization of the assimilate (16, 18). Inhibition of assimilate translocation by water stress has been observed in a number of plant species (6,7,11,13 Disagreement exists as to the relative sensitivity of photosynthesis and translocation to water stress. Several studies have concluded that translocation is more sensitive to water deficits than is photosynthesis (6, 7). In contrast to these conclusions, others (11,13,14,19,20) have suggested that photosynthesis is more sensitive to water stress than translocation. Wardlaw (19) has indicated that the effect of water stress on the translocation process is related to the availability of photosynthate more so than by a direct effect on the translocation process mechanism per se.The objective of this study was to define the relationship between leaf water status, photosynthesis, and translocation of current assimilate as a function of photosynthetic type (C3 versus C4) and growth stage. MATERIALS AND METHODSSorghum (Sorghum bicolor L. Moench) and cotton (Gossypium hirsutum L. cv. SP 37) were chosen for study due to differences in photosynt...