P. J. C. Kuiper

The effect of low root temperature on growth and lipid composition of low temperature tolerant rootstock genotypes for cucumber

In the framework of research directed to diminish energy consumption of glasshouse cucumber production, three low temperature tolerant rootstock genotypes for cucumber were compared. Firstly, growth at low root temperature of one Cucurbita ficifolia and two Sicyos angulatus genotypes was studied to determine which was the one most suitable as a cucumber rootstock at suboptimal root temperatures. Secondly, differences in lipid composition were examined. Thirdly, lipid composition of these rootstock genotypes was compared with that of low temperature sensitive cucumbers (Cucumis sativus L.; cv. Farbio and CPO inbred lines 79345 and 81354) studied earlier, to determine whether observed differences in lipid composition were consistent with differences in growth at low temperature of related species. Plants were grown at an air temperature of 20-degrees-C d/12-degrees-C n and at constant root temperatures of 20-degrees-C, 16-degrees-C or 12-degrees-C. Although growth decreased at 12-degrees-C for all genotypes, both Sicyos angulatus genotypes were more tolerant to low root temperature than Cucurbita ficifolia. Low root temperature affected root lipid composition only. An increased phospholipid and a markedly lower sterol and sterol ester level resulted in a strongly decreased sterol/phospholipid ratio at 12-degrees-C. Growth at low root temperature was inversely related with the sterol/phospholipid ratio but no correlation between growth and sterol/phospholipid ratio of the rootstock genotypes within one temperature regime was observed. So, this ratio is not an appropriate selection criterion for growth capacity.

Effects of N management on growth, N2 fixation and yield of soybean

Soybean (Glycine max) is one of the most importantfood and cash crops in China. Although soybean has the capacity to obtain alarge proportion of its N from N2 fixation, it is commonfarmers practice to apply an N top dressing to maximize grain yield. Afield experiment was conducted to study the effects of N application as urea atvarious stages during the vegetative and reproductive phases on crop biomass,N2 fixation and yield of two soybean genotypes, Luyuebao and Jufeng.Starter N at 25 kg ha−1 resulted in minimumbiomass and pod yield while starter N at 75 kgha−1 had no significant effect and N top dressing, ateither the R1 or R5 stage, resulted in increased biomass and pod yield. Maximumbiomass and pod yield were obtained when a top dressing of 50 kgha−1 was applied at the flowering stage. The effects oftop dressing on the capacity to fix N2 were complex. The proportionof plant N derived from N2 fixation (Pfix) was highest when onlystarter N at 25 kg ha−1 was applied. Any topdressing reduced nodulation and Pfix, but increased biomass, so that totalN2 fixed increased for top dressing at the flowering or pod fillingstage. Common farmers practice of applying 75 kg Nha−1 at the V4 stage, resulted in a significantreduction in N2 fixation. To evaluate the application of Nfertilization at various stages ofdevelopment on growth, nodulation and N2 fixation in more detail, anexperiment in nutrient solution with or without 20 mMNO3− was conducted with genotype Tidar. The N-freetreatment gave the lowest biomass and total N accumulation, as in the fieldexperiment. A continuous nitrate supply resulted in the highest biomass,associated with an increase in total leaf area per plant, maximum individualleaf area, branch and node number per plant, shoot/root ratio and leaf arearatio, compared to the N-free treatment. R1 was the most responsive stage fornitrate supply as well as for interruption of the nitrate supply. Since theresults from the field experiment were in agreement with thosefrom the experiment in nutrient solution in a greenhouse, the latter can beusedto predict crop performance in the field.

GLUTATHIONE, A TRIPEPTIDE WHICH MAY FUNCTION AS A TEMPORARY-STORAGE COMPOUND OF EXCESSIVE REDUCED SULFUR IN H2S FUMIGATED SPINACH PLANTS

SummaryExposure of spinach plants to 250 ppb H2S for two days resulted in a four-fold increase of the reduced glutathione (GSH)/sulphydryl (SH) concentration and in a two-fold increase of the oxidized glutathione (GSSG) concentration of the shoots. Both in the presence and the absence of H2S, glutathione was predominantly present in the reduced form (more than 86%). When the H2S exposure was ceased both the levels of GSH and GSSG in the shoot rapidly decreased. There was no emission of H2S by the leaves after the fumigation was terminated. Glutathione reductase activity in the shoots was not affected by short term H2S fumigation. It is proposed that glutathione plays the role of a temporary storage compound of excessive reduced sulphur in spinach shoots when exposed to H2S in the ambient air.

Fatty acid composition and chlorophyll content of epiphytic lichens and a possible relation to their sensitivity to air pollution.

Fatty acid composition and chlorophyll content of thirteen epiphytic lichen species were determined and related to the air pollution sensivity of the lichens based upon field observations. A direct relation between the chlorophyll content and, to a lesser extent, the degree of unsaturation of the fatty acids of the lichen species and the sensitivity to air pollution was demonstrated. It is suggested that the sensitivity of lichens to air pollution is related to the degree of dependency of the mycobiont on the phycobiont as far as metabolic energy is concerned; in such a way that the stronger this dependency is, the more sensitive the lichen will be to air pollution.

Physiological response of soybean genotypes to plant density

Response of soybean (Glycine max (L.) Merr.) to plant density has occupied a segment of agronomic research for most of the century. Genotype differences have been noted especially in response to planting date, lodging problems and water limitation. There is limited information on the physiological growth parameters (such as relative growth rate, leaf area ratio, specific leaf area ratio and shoot/root) that corresponds to different soybean genotypes response to different plant densities and how these parameters affect plant yield. The purpose of this study was to investigate the effect of plant density on biomass production, N2 fixation and yield of different soybean genotypes by comparing the current farmer’s practice to other planting densities in the field. Further experiments in controlled climatic condition studied the physiological changes of growth parameters to different plant densities by different soybean genotypes. The result of the field experiment showed that total biomass, plant N derived from N2 fixation and seed yield of all three genotypes responded positively to increased plant density. Double density significantly increased seed yield per unit of area, by 93, 37 and 43% for the determinate Wuyin9, the semi-determinate You91-19 and the indeterminate Jufeng, respectively. The effect of plant density on individual plant characteristics varied in this experiment. Double density had no significant effect on individual plant biomass and seed weight per plant in the determinate genotype Wuyin9, but had a significant negative effect in the later maturing genotypes, with a reduction of 19% in biomass for both determinate Jufeng and semi-determinate You91-19. Detailed experiments under controlled climatic conditions in a growth chamber and a greenhouse in nutrient solution and soil were conducted to determine the physiological variations of growth parameters between the different soybean genotypes in response to plant density. The results showed that the negative response of the individual indeterminate Jufeng plant to planting at double density was mainly due to increases in leaf area ratio (LAR) and specific leaf area (SLA). The greenhouse experiments gave results similar to those obtained in the field. Double density had no significant effect on growth and yield of individual plants of the determinate genotype Luyuebao while it significantly decreased both biomass and yield of individual plants by 40% for semi-determinate You91-19 and 46–47% for indeterminate Jufeng, respectively. For all genotypes, yield per unit of area was higher at double than at single density. Seed yield reduction at single density was mainly associated with a decrease in pod or seed number per unit of area.

NaCl effects on root plasma membrane ATPase of salt tolerant wheat

Wheat seedlings of a salt tolerant cultivar were grown hydroponically in presence and absence of 100 mM NaCl. Roots were harvested, and the plasma membrane (PM) fraction was purified. PM ATPase required a divalent cations for activity (Mg > Mn > Ca > Co > Zn > Ni > Cu), and it was further stimulated by monovalent cations (K > Rb > NH4 > Li > choline > Cs). The pH optima were 6.0 and 5.6 in absence and presence of 25 mM KCl, respectively. The enzyme was sensitive to vanadate and DCCD but insensitive to azide, oligomycine and nitrate. The enzyme displayed a high preference for ATP but was also able to hydrolyze other nucleotide tri- and diphosphates. The enzyme activity showed a simple Michaelis-Menten kinetics for the substrate Mg2+-ATP in both control and salt exposed roots. The polypeptide patterns of control and salt stressed PM fractions, detected by SDS-PAGE, were very similar. NaCl substantially reduced the PM ATPase specific activity, whereas it had little effect on the apparent Km for Mg2+-ATP. Since the root PM ATPase of salt sensitive and resistant genotypes responded similarly to salinity stress, it seems unlikely that the mechanism of salt tolerance in wheat is primarily based on differences in PM ATPase characteristics.

GROWTH TEMPERATURE AND LIPID-COMPOSITION OF CUCUMBER GENOTYPES DIFFERING IN ADAPTATION TO LOW-ENERGY CONDITIONS

Summary Total lipid, phospholipid and fatty acid composition of leaf and root as well as leaf PG fatty acid composition were determined for two low temperature tolerant inbred lines of cucumber ( Cucumis sativus L.) and a control variety, all grown at two temperature regimes. Hardly any genotypic differences were observed at either temperature regime. At low temperature the degree of unsaturation of fatty acids increased. There was no correlation between fatty acid composition of PG and genotypical differences in growth. However, at low temperature the inbred lines reacted by lowering the amount of PG without changing the proportion of relatively saturated PG fatty acids, while the control variety reacted by lowering the proportion of relatively saturated PG fatty acids at a stable PG content. In general, no valid selection criterion based on lipid composition was found, indicating that lipid composition at present shows no promise as a suitable selection criterion for genetic adaptation to low temperature conditions.

Ca2+- and Mg2+-ATPase activities in winter wheat root plasma membranes as affected by NaCl stress during growth

Summary Winter wheat seedlings were grown in Hoagland nutrient solution with or without 100 mmol/L NaCl added. Plasma membranes from root cells were prepared by aqueous polymer two phase partitioning and the stimulation of plasma membrane ATPase activity by Mg 2+ and Ca 2+ was investigated. The enzyme was activated by Mg 2+ or Ca 2+ and Mg 2+ -ATPase was further stimulated by K + , whereas no such stimulation was observed with Ca 2+ -ATPase. Ca 2+ inhibited Mg 2+ -ATPase activity. pH optima for Mg 2+ - and Ca 2+ -ATPase activities were 6 and 5.6, respectively. ATPase activated by Mg 2+ was inhibited by vanadate and DCCD, while Ca 2+ -ATPase was less sensitive. ATP was the preferred substrate but other nucleotide tri- and diphosphates were also hydrolyzed by the plasma membrane ATPases. NaCl stress during growth had no major effect on the plasma membrane polypeptide components. Simple Michaelis-Menten kinetics were found when Mg 2+ - or Ca 2+ -ATP was used as substrate for both control and salt stressed roots. NaCI markedly reduced the V max of Mg 2+ - and Ca 2+ -ATPase activities while it had little effect on the apparent K m for Mg 2+ - or Ca 2+ -ATP. NaCl-induced reduction of V max of ATPase activity correlated with NaCl-altered plasma, membrane lipid composition and the role of the lipid environment in ATPase activity is discussed.

The effect of temperature on early growth of cucumber genotypes differing in genetic adaptation to low-energy conditions

Abstract Growth characteristics were determined of cucumber lines (Cucumis sativus L.) selected for increased growth at sub-optimal temperature conditions and of a control (cultivar ‘Farbio’). Plants were grown in controlled environments on nutrient solution at optimal ( 25 20° C ) and sub-optimal ( 20 12° C ) day/night temperatures. Stem length, leaf area and fresh and dry weight of leaves, stem and roots were determined at 5 harvest dates. Multivariate analysis of variance showed significant differences between the temperature regimes for all genotypes tested and in all growth characteristics except net assimilation rate. As related to temperature regime, significant differences were present in morphology and distribution of dry matter over stem, roots and leaves between ‘Farbio’ and the low-energy lines. Genotype × temperature interactions occurred for leaf area ratio and stem length. In general the low-energy lines showed increased growth as compared with ‘Farbio’. Growth differences observed in mature plants were already present at an early stage of development. It is concluded that young plants are suitable for further physiological investigations to establish criteria for early selection of cucumber genotypes with a high energy efficiency.

Aluminium tolerance of the velvet beans Mucuna pruriens var. utilis and Mucuna deeringiana

Although Al is generally regarded a nonessential element, in nutrient solution studies at pH 4.2 with NO3 as nitrogen source an Al3+concentration of 0.33 meqL−1, increased root fresh weight of M. p. utilis and M. deeringiana but not shoot fresh weight. The two species did not differ essentially in their response to aluminium.