High Root Temperature Research Articles

Accumulation of starch in wheat grain under different shoot/root temperatures during maturation.

The impact of high temperatures on accumulation of starch in the grain of wheat (Triticum aestivum L.) is usually attributed to direct effects of the stress on the enzymes involved. However, roots are extremely sensitive to temperatures that can be as high as those experienced by the shoots, and their role in whole-plant responses should be considered. Wheat (cv. Len) was grown at 15/15, 30/15, 15/30, and 30/30˚C shoot/root temperatures during maturation, and accumulation of dry matter and N, contents of sucrose and starch, and activities of enzymes in the pathway of starch assimilation in the endosperm, were measured weekly. Dry matter and N accumulation were affected more by root than by shoot temperatures. High whole-plant temperatures (30/30˚C) accelerated linear grain growth but diminished the duration of assimilation, the contents of sucrose and starch, and the activities of the enzymes involved. The effects of high root temperature (15/30˚C) resembled those of high whole-plant temperature, whereas low root temperature (30/15˚C) tended to ameliorate them. Sucrose synthase and soluble starch synthase were affected more than the other enzymes by high shoot and/or root temperature. However, treatments that caused the lowest activities resulted in the fastest, but briefest, linear rates of grain growth. We concluded that shoots and roots interact in the response of wheat to high temperature, and that stress on both organs affects accumulation of starch in grain.

Root growth and nutrient element status of creeping bentgrass cultivars differing in heat tolerance as influenced by supraoptimal shoot and root temperatures

This study was designed to determine and compare root growth and nutritional responses of creeping bentgrass cultivars that differ in heat tolerance to differential, supraoptimal, shoot and root temperatures. Shoots and roots of ‘Penncross’ (heat sensitive) and ‘L‐93’ (heat tolerant) were exposed to four air/soil temperature regimes (20/20°C‐control, 20/35°C, 35/20°C, and 35/35°C) in water baths and growth chambers. Exposing roots to supraoptimal root temperature (35°C) while maintaining shoots at normal temperature (20°C) or particularly at 35°C reduced root fresh weight, root number, and contents of nitrogen (N), phosphorus (P), and potassium (K) in shoots and roots and accelerated root death for both cultivars. High root temperature had greater detrimental effects on root growth and nutrient element accumulation than high shoot temperature for both cultivars. A low root temperature at supraoptimal shoot temperature improved root growth, reduced root mortality; and increased N, P, and K contents in shoots and roots. Among the three nutrient elements, K was the most sensitive to changes in root temperature. L‐93 generally maintained higher fresh weight and number of roots and higher N, P, and K contents in shoots and roots, particularly K in roots, under high root (20/35°C) or shoot/root (35/35°C) temperatures. The results indicated that root growth and nutrient element accumulation, particularly of K, played an important role in creeping bentgrass tolerance to heat stress imposed on shoots by high air temperature or to roots by high soil temperatures. The enhanced root growth and nutrient element relations with a low root temperature at supraoptimal ambient temperatures could lead to the improved shoot growth in cool‐season grasses observed under these conditions.

142 Root Mortality and Nutrient Uptake of Creeping Bentgrass in Response to Differential Root and Shoot Temperatures

This study was designed to compare and determine root growth and nutritional responses of creeping bentgrass cultivars that differ in heat tolerance to deferential, supraoptimal shoot and root temperatures. Shoots and roots of `Penncross' (heat sensitive) and `L-93' (heat tolerant) were exposed to four differential air/soil temperature regimes (20/20-control, 20/35, 35/20, and 35/35 °C) in water baths and growth chambers. Exposing roots to supraoptimal root temperature (35 °C) while maintaining shoots at normal temperature (20 °C), or at 35 °C in particular, reduced root fresh weight, root number, the content of N, P, and K in shoots and roots, and accelerated root death for both cultivars. High root temperature had a greater detrimental effects on root growth and nutrient accumulation than high shoot temperature for both cultivars. Reducing root temperature at supraoptimal shoot temperature improved root growth, reduced root mortality, and increased N, P, and K content in shoots and roots. Among the three nutrient elements, K was the most sensitive to changes in root temperature. L-93 generally maintained higher root fresh weight and number, and N, P, K content in shoots and roots, particularly K in roots, under high root (20/35 °C) or shoot/root (35/35 °C) temperatures. The results indicated that root growth and nutrient accumulation, particularly K, played an important role in creeping bentgrass tolerance to heat stress imposed to shoots by high air temperature or to roots by high soil temperatures. Reducing root temperature under supraoptimal ambient temperatures enhanced root growth and nutrient relations, and thus could lead to the improved shoot growth in cool-season grasses as reported previously.

Development of Frost Tolerance in Winter Wheat as Modulated by Differential Root and Shoot Temperature

Abstract: Winter wheat plants (Triticum aestivum L. cv. Urban), grown in nutrient solution, were exposed to differential shoot/root temperatures (i.e., 4/4, 4/20, 20/4 and 20/20 d̀C) for six weeks. Leaves grown at 4d̀C showed an increase in frost tolerance from ‐ 4d̀C down to ‐ 11 d̀C, irrespective of root temperature. In 4/20 d̀C plants, high root temperature decreased the rate of hardening of the leaves, but did not influence the final level of frost tolerance. In roots grown at 4d̀C frost tolerance increased from ‐ 3 d̀C down to ‐ 4 d̀C, independently of shoot temperature. An accumulation of soluble sugars in the leaves was only observed when both shoot and root were grown at 4d̀C and was not correlated with final frost tolerance achieved. However, the rate of hardening was correlated with the soluble sugar concentration. An increase in root soluble sugar concentration was exclusively observed in roots exposed to a temperature of 4d̀C, irrespective of shoot temperature. Proline concentration only increased in plant parts exposed to a temperature of 4d̀C. The present results indicate that the importance of root temperature in low‐temperature hardening of winter wheat is limited, even though exposure to differential root and shoot temperatures brought about pronounced changes in growth, soluble sugar concentration, insoluble sugar concentration and proline concentration in roots and leaves.

Development of Frost Tolerance in Winter Wheat as Modulated by Differential Root and Shoot Temperature

Abstract: Winter wheat plants (Triticum aestivum L. cv. Urban), grown in nutrient solution, were exposed to differential shoot/root temperatures (i.e., 4/4, 4/20, 20/4 and 20/20 d̀C) for six weeks. Leaves grown at 4d̀C showed an increase in frost tolerance from - 4d̀C down to - 11 d̀C, irrespective of root temperature. In 4/20 d̀C plants, high root temperature decreased the rate of hardening of the leaves, but did not influence the final level of frost tolerance. In roots grown at 4d̀C frost tolerance increased from - 3 d̀C down to - 4 d̀C, independently of shoot temperature. An accumulation of soluble sugars in the leaves was only observed when both shoot and root were grown at 4d̀C and was not correlated with final frost tolerance achieved. However, the rate of hardening was correlated with the soluble sugar concentration. An increase in root soluble sugar concentration was exclusively observed in roots exposed to a temperature of 4d̀C, irrespective of shoot temperature. Proline concentration only increased in plant parts exposed to a temperature of 4d̀C. The present results indicate that the importance of root temperature in low-temperature hardening of winter wheat is limited, even though exposure to differential root and shoot temperatures brought about pronounced changes in growth, soluble sugar concentration, insoluble sugar concentration and proline concentration in roots and leaves.

Potato performance in response to different mulches. 1. Nitrogen metabolism and yield.

This work evaluates the impact that the application of different mulches exerts on nitrogen (N) metabolism in roots and leaves and on yield of potato tubers (Solanum tuberosum var. Spunta). The parameters analyzed in this experiment were root temperature; nitrate reductase and nitrite reductase activities; concentrations of nitrates, ammonium, amino acids, proteins, and organic N; dry weight of roots and leaves; and tuber yield. Use of white polyethylene (T2) and white-black plastic (T3) promoted optimal root temperatures for plant growth (23-27 degrees C). Under these experimental conditions, plants showed the greatest efficiency in N utilization and the greatest yield in tubers. Considering the sensitivity of this plant to thermal stress, high root temperatures caused by black polyethylene (>31 degrees C) (T4) depressed N metabolism as well as yield, compared with the results of T2 and T3. Finally, clear polyethylene plastic (T1) caused more damage than did the absence of mulch (control, T0).

Root temperature effects on growth and bud break of Rosa hybrida in relation to cytokinin concentrations in xylem sap

The effects of three divergent root temperatures (11°C, 20°C and 26°C) on growth and bud break of Rosa hybrida were studied. Root morphology was changed considerably with root temperature. Roots at 11°C were white, succulent, short and sparsely branched, whereas at 26°C roots were long, brown, thin and branched. However, root dry weight was not affected by root temperature. Axillary bud break was earlier at higher root temperatures, resulting in a higher shoot dry weight. At higher temperatures, bottom breaks tended to appear earlier. Our hypothesis was that the effect of root temperature on growth and bud break of the shoot is mediated by cytokinin production in the roots and/or cytokinin translocation to the shoot. The concentration of zeatin riboside (ZR) in bleeding sap was determined during plant development. ZR was found to decrease slightly after bud break, but was not affected by the root temperature treatments, which falsified our hypothesis. Other processes may be involved in the effect of root temperature on shoot growth and bud break.

Root System Activity of Fruit Trees in Response to Shoot Pruning, High Temperature, and Excess Water

Relationship between root system and shoot pruning was studied by three different pruning times (February, June, and August) and intensity (heavy, medium, and light) using satsuma mandarin trees (Citrus unshiu Marc.). Root weight, respiratory rate of fine root, and CO2 concentration in root zone were measured on the 90th day after starting each pruning treatment. The weight of fine root was more severely influenced by pruning intensity than by pruning time. Fine root of heavy pruned trees showed lower respiratory rate than those of medium- and light-pruned trees. Heavy-pruned trees showed the highest CO2 concentration level in root zone. Influence of high root temperature on root respiration was investigated using `Kyoho' grape (Vitis vinifera L. × V. Iabrusca L.), kiwifruit (Actinidia deliciosa), and satsuma mandarin trees. Respiratory rate of grape root increased more rapidly than those of mandarin and kiwifruit under high root temperature. Respiratory rate of mandarin root given immersion treatment in stagnated water began to decrease significantly at the 70th hour after starting the treatment. Photosynthesis of the trees decreased by 85% at the same time.

Root System Activity of Fruit Trees in Response to Shoot Pruning, High Temperature, and Excess Water

Relationship between root system and shoot pruning was studied by three different pruning times (February, June, and August) and intensity (heavy, medium, and light) using satsuma mandarin trees (Citrus unshiu Marc.). Root weight, respiratory rate of fine root, and CO2 concentration in root zone were measured on the 90th day after starting each pruning treatment. The weight of fine root was more severely influenced by pruning intensity than by pruning time. Fine root of heavy pruned trees showed lower respiratory rate than those of medium- and light-pruned trees. Heavy-pruned trees showed the highest CO2 concentration level in root zone. Influence of high root temperature on root respiration was investigated using `Kyoho' grape (Vitis vinifera L. × V. Iabrusca L.), kiwifruit (Actinidia deliciosa), and satsuma mandarin trees. Respiratory rate of grape root increased more rapidly than those of mandarin and kiwifruit under high root temperature. Respiratory rate of mandarin root given immersion treatment in stagnated water began to decrease significantly at the 70th hour after starting the treatment. Photosynthesis of the trees decreased by 85% at the same time.

Effects of Root Temperatures on Leaf Gas Exchange and Growth at High Air Temperature in Phaseolus acutifolius and Phaseolus vulgaris

Heat stress influences plant growth, development, and productivity. This research was initiated to determine whether differential root sensitivity to heat is important in determining differences in plant heat tolerance. Tepary bean (Phaseolus acutifolius Gray) and heat tolerant (GNUI 59) and heat sensitive (BBL 47) genotypes of common bean (P. vulgaris L.) were used to study leaf gas exchange and growth after exposure to high air temperature combined with either high or low root temperature. The effect of temperature on endogenous abscisic acid (ABA) levels in leaves and roots was determined using an enzyme‐immunoassay technique. High shoot/root temperature (45/45°C) for 5 h reduced carbon exchange rate (CER) and subsequent growth in all genotypes. Maintaining root temperature at 25°C restored CER to nearly the control level. High root temperature decreased endogenous ABA levels in the roots in all genotypes, but increased ABA in the leaves in the tepary bean and BBL 47 without stomatal closure. Water stress or exogenous ABA pretreatment prior to high temperature treatment induced stomatal closure at high air temperature. There were no differences in leaf temperatures between the two root temperatures, suggesting that the lower levels of CER, mesophyll conductance, and growth under high root temperature were due to root rather than to leaf temperature.

Response of sand‐grown tomato supplied with varying ratios of nitrate/ammonium to constant and variable root temperatures

Abstract Tomato (Lycopersicon esculentum Mill.) is commercially grown in a wide range of climatic conditions. There is a need to understand nutrient uptake by tomato at various climatic conditions in order to devise the specific nutrient supply to this important crop. Tomato seedlings, at the first flower blooming stage, were transplanted into 6‐L pots of washed sand. Four root temperature regimes (day/night, °C) 12/12, 16/08, 17/17, and 30/20, and four temperatures of the shoots 20/20, 25/25, 25/15, and 30/20 were controlled separately for the shoots and roots. All four growth cabinets had the same day length of 13 h and light intensity of 400 μmole/m2/s measured on top of the canopy, The relative humidity was 85%. The nutrient solutions contained 10 mM N in three ratios of nitrate:ammonium (NO3:NH4)—10:0, 8:2, and 6:4 each in three replications in each growth cabinet. The water consumption, fresh and dry weight, water soluble nutrient in the plant, exudate composition at the end of the experiment and total mineral composition in the shoots were determined. The transpiration ratio for the high root temperatures was 190 g H2O/g DM. Based on rate of water uptake, plant growth on the 16/08°C root regime was significantly higher than that of 12/12°C root regime, despite the fact that the average temperature on time was the same in both treatments. Low root temperatures decreased the concentrations of cations in the plant but had no effect on the balance between cations and anions (C‐A). Increasing NH4 proportion decreased C‐A in the plant. At root temperature of 12°C, potassium (K) and NO3 were present at high concentration in the exudate but soluble NO3 in the shoot was the lowest. The result suggests that nitrate reduced in the shoot produced organic anions that are left in the shoot and their charge balance that on K, due to slow root growth at low temperatures. Higher DM was produced by the NO3 only form at low variable root temperature than in the treatments that contained NH4. At low root temperature, the K selectivity against sodium (Na) was reduced. This suggest that, at low root temperatures, high K concentration in the nutrient solution might he needed.

Effect of supraoptimal root temperature on the growth, root respiration and sugar content of cucumber plants

The effects of high root temperature on plant growth, leaf elemental composition, root respiration and sugar content in cucumber plants ( Cucumis sativus L. cultivar ‘Sharp I’) were studied. Root dry weight, leaf area and leaf concentrations of most nutrient elements were all reduced as the root temperature was raised to 35°C, and to 38°C in particular. High root temperature markedly enhanced intact root respiration. This increase of root respiration was due to the stimulation of the alternative respiration. On the other hand, the cytochrome respiration deteriorated at high root temperatures. However, ATP content was not much different between the roots grown at 25° and 38°C. With the rise of root temperature, root sugars, particularly raffinose, greatly increased, while root pectin content decreased. High root temperature also adversely affected the levels of malic and fumaric acids in the roots. It is suggested that disturbance of carbohydrate metabolism in the root is a primary factor responsible for the growth inhibition and dysfunctions of cucumber roots grown at supraoptimal root temperatures.

Partition of photosynthates between shoot and root in spring wheat (Triticum aestivum L.) as a function of soil water potential and root temperature

Low soil water potential and low or high root temperatures are important stresses affecting carbon allocation in plants. This study examines the effects of these stresses on carbon allocation from the perspective of whole plant mass balance. Sixteen-day old spring wheat seedlings were placed in a growth room under precisely controlled root temperatures and soil water potentials. Five soil water potential treatments, from −0.03 MPa to −0.25 MPa, and six root temperature treatments, from 12 to 32°C were used. A mathematical model based on mass balance considerations was used, in combination with experimental measurements of rate of net photosynthesis, leaf area, and shoot/root dry masses to determine photosynthate allocation between shoot and root. Partitioning of photosynthates to roots was the lowest at 22–27°C root temperature regardless soil water potential, and increased at both lower and higher root temperatures. Partitioning of photosynthates to the roots increased with decreasing soil water potential. Under the most favourable conditions, i.e. at −0.03 MPa soil water potential and 27°C root temperature, the largest fraction, 57%, of photosynthates was allocated to the shoots. Under the most stressed conditions, i.e. at −0.25 MPa soil water potential and 32°C root temperature, the largest fraction, more than 80%, of photosynthates was allocated to roots.

COMBINED IRRIGATION AND FERTILIZATION IN ARID ZONES

Sand dunes and highly calcareous soils occupy vast areas in arid zones. The soils are characterized by low available nutrient content and low to medium water-holding capacity of the upper soil surface. These features result in low vegetation density under arid climate conditions. The introduction of trickle irrigation coupled with liquid fertilizers turned desert sand dunes and highly calcareous soils into productive agricultural soils for high cash crops. The intensity of daily nutrient supply dictates the farmer's consideration of the form of nitrogen supplied to the crop and to the variable sensitivity of plants to the different forms of N supplied by various fertilizers through the irrigation system. The combination of high root temperature and high ammonium concentration is of particular importance. Plants that have relatively low carbohydrate content in their roots might suffer from ammonia toxicity if a high daily supply of ammonium is available. High concentrations of urea and very high calcium carbonate content in the soil are also dangerous to ammonium- sensitive plants like tomatoes. Planning the irrigation system and nutrient supply to the crops according to their physiological stage of development, and consideration of the soil and climate characteristics, can give high yields and high quality crops with minimum pollution, but salt accumulation on the soil surface should be prevented, either by sprinkle irrigation, or by plastic mulch during the growing season.

キュウリの光合成, 根への光合成産物の転流とその代謝に及ぼす高根温の影響

Cucumber plants (Cucumis sativus L. cv. Sharp I) with 3 leaves were grown in hydroponics at root temperatures of 25°, 32°, 35° and 38°C for up to 9 days. The rates of photosynthesis and transpiration as well as leaf chlorophyll content was not affected by the root temperatures from 25° to 35°C. In plants grown at 38°C the rates of photosynthesis and transpiration were unaffected over the first 5 days, but a large decrease occurred in the two parameters as well as chlorophyll content after 9 days. When a shoot was pulse-fed with 14CO2 after 6 days growth at 25° or 38°C root temperatures, translocation of 14C-photosynthates to the roots during a 10-h chase in darkness was faster at 38°C than it was at 25°C. However, the amounts of the 14C accumulated per unit dry weight of root tissue were not different between the two treatments, becuase of an increased carbon loss by respiration of the roots at 38°C. At 38°C, more 14C was allocated to soluble C than to insoluble C; the reverse was the case at 25°C. Fractionation of soluble 14C into sugars, organic acids, and amino acids revealed that in the roots at 38°C, a very large proportion of 14C was in the sugar fraction, particularly raffinose. This was in contrast to the 25°C roots in which the soluble 14C was distributed evenly to the three fractions. Possible relationships of the changes in photosynthesis and photosynthate translocation and metabolism in the roots with root growth and functions under the high root temperature conditions are discussed

Phytophthora cryptogea root rot of tomato in rockwool nutrient culture:

SUMMARYThe effect of root temperature on growth and yield of rockwool‐grown tomato plants infected with Phytophthora cryptogea was investigated. Measurements of shoot and root growth were taken at high (25oC) and low (15oC) root temperatures during the generative phase of growth. The growth of roots of healthy and P. cryptogea‐infected tomato plants in rockwool blocks was higher in plants grown with roots at 25oC than at 15oC after 60 days and a similar effect was found in slabs after 98 days. Under sub‐optimal conditions for growth the disease became severe when root temperatures were low. Growth of roots was greatest when roots were maintained at a high temperature in combination with an ambient air temperature of c. 15oC and the response was greater in cv. Counter than cvs Calypso and Marathon. Water‐soluble carbohydrates of roots were higher in those produced in blocks than slabs and were reduced by infection compared to healthy plants with roots at 15oC and 25oC. Reduced transpiration rates were found 17 days after inoculation in symptomless plants grown at a root temperature of 25oC. Infection, regardless of the temperature of the roots or cultivar, led to reduced stem growth. The plants grown at 25oC were taller than those with a root temperature of 15oC. After 9 wk of harvest, the cumulative fruit yields in infected cvs Counter and Calypso grown at 25oC were comparable to that in healthy plants grown at either temperature and cumulative fruit numbers followed a similar pattern. High root temperatures led to delayed fruit ripening between weeks 3–10 and a larger number of unripe fruit. The weight of unripe fruit from infected plants grown at 25oC at the terminal harvest was higher than from healthy plants with roots maintained at 15oC.

Effect of high root temperature on Bradyrhizobium-peanut symbiosis

Three strains of Bradyrhizobium, 280A, 2209A and 32H1, that nodulated peanuts (Arachis hypogaea L.), were tested for their ability to grow and survive at elevated temperatures of up to 42°C in laboratory culture. Strain 32H1 was unable to grow at 37°C and was more sensitive to elevated temperatures than the other two strains. All three produced heat-shock proteins of molecular weights 17 kDa and 18 kDa. Two greenhouse experiments were conducted to determine the effect of high root temperature on nodulation, growth and nitrogen fixation of peanut. Two peanut varieties (Virginia cv NC7 and Spanish cv Pronto) were inoculated and exposed to root temperatures of 30°, 37° and 40°C. Nodulation and nitrogen fixation were strongly affected by root temperature but there was no variety × temperature interaction. At a constant 40°C root temperature no nodules were formed. Nodules were formed when roots were exposed to this temperature with diurnal cycling but no nitrogen fixation occurred. Highest plant dry weight, shoot nitrogen content and total nitrogen were observed at a constant root temperature of 30°C. Increasing root temperature to 37°C reduced average nitrogen content by 37% and total nitrogen by 49% but did not reduce nodulation. The symbiotic performance of the strains corresponded to their abilities to grow and survive at high temperature in culture.

Root-zone temperature and salinity: Interacting effects on tillering, growth and element concentration in barley

The effects of root-zone salinity (0, 30, and 60 mmol L−1 of NaCl) and root-zone temperature (10, 15, 20, and 25°C) and their interactions on the number of tillers, total dry matter production, and the concentration of nutrients in the roots and tops of barley (Hordeum vulgare L.) were studied. Experiments were conducted in growth chambers (day/night photoperiod of 16/8 h and constant air temperature of 20°C) and under water-culture conditions. Salinity and root temperature affected all the parameters tested. Interactions between salinity and temperature were significant (p<0.05) for the number of tillers, growth of tops and roots, and the concentration of Na, K, P in the tops and the concentration of P in the roots. Maximum number of tillers and the highest dry matter were produced when the root temperature was at the intermediate levels of 15 to 20°C. Effect of salinity on most parameters tested strongly depended on the prevailing root temperature. For example, at root temperature of 10°C addition of 30 mmol L−1 NaCl to the nutrient solution stimulated the growth of barley roots; at root temperature of 25°C, however, the same NaCl concentration inhibited the root growth. At 60 mmol L−1, root and shoot growth were maximum when root temperature was kept at the intermediate level of 15°C; most inhibition of salinity occurred at both low (10°C) and high (25°C) root temperatures. As the root temperature was raised from 10 to 25°C, the concentration of Na generally decreased in the tops and increased in the roots. At a given Na concentration in the tops or in the roots, respective growth of tops or roots was much less inhibited if the roots were grown at 15–20°C. It is concluded that the tolerance of barley plant to NaCl salinity of the rooting media appears to be altered by the root temperature and is highest if the root temperature is kept at 15 to 20°C.

The effect of high temperature on Vigna radiata nodulation and growth with different bradyrhizobial strains

A study was conducted to examine the effect of constant high temperatures and diurnally administered temperature regimes (day/night temperature was maintained at 30°C and increasing 2 hr temperature shocks of 36, 42 and 48°C were applied daily) on growth, nodulation and nitrogen fixation of mungbean ( Vigna radiata L. Wilczek) plants and growth responses of five different cowpea bradyrhizobial strains. Mungbean genotype and bradyrhizobial strains responded differently to high temperatures. Mungbean plants survived at (1) diurnal regimens of high temperature and (2) constant root temperatures of 42 and 48°C (day and night), but germination at 48°C was reduced to 38%. The bradyrhizobial strains survived, grew and remained infective and effective after incubation at constant temperatures up to 42°C and diurnal regimen high temperatures. Two strains, Vml and Vrl16, survived and multiplied at a constant temperature of 48°C. These strains were also effective on mungbean and siratro ( Macroptilium alropurpureum) plants after incubation at 48°C for 5–10 days. Elevated temperatures (36°C) depressed nodulation and nitrogen fixation. Constant high temperatures (42 and 48°C) at the seedling stage markedly affected nitrogenase activity (ARA).

HONEY LOCUST SEEDLING DEVELOPMENT DURING OSMOTIC AND HIGH ROOT TEMPERATURE STRESS

Development of half-sib Gleditsia triacanthos inermis Willd. (honey locust) seedlings was studied during exposure to osmotic and high root temperature stress. Seven days after seed scarification, seedlings of uniform fresh weight were transferred to static hydroponic culture vessels in a growth chamber. Three days later, vessel solutions were replaced with polyethylene glycol 8000-amended solutions with osmotic potentials (ψπ) of -0.05, -0.10, or -0.20 MPa at 23C. Within each ψπ treatment, root temperature was increased from ambient (23C) to 35C for 0, 6, 12, or 24 hr day-1 for 20 days. Root and shoot dry weights decreased with increasing exposure to 35C among seedlings in the -0.05 MPa solution and decreased for seedlings in -0.10 and -0.20 MPa solutions in all temperature regimes. Epicotyl expansion tended to decrease with decreasing ψπ and increasing exposure to 35C. However, for plants in the -0.20 MPa solution, epicotyl length was greatest when roots were exposed to 35C for 6 hr day-1.