Shamouti orange (Citrus sinensis L. Osbeck) salt-tolerant cells were grown under low water potential conditions induced by polyethylene glycol (PEG), NaCl, and CaC12. On the basis of equal osmotic potentials, PEG was the least inhibitory, NaCI next, and CaC12 the most inhibitory. The relation between growth capacity and ion content can be summarized as follows. (a) Internal K' concentration was a major factor which changed in the presence of PEG, NaCl, and CaC12 and probably played a key role in determining growth capacity. (b) Internal concentrations of Na', Ca2l, or Cl-could not be directly correlated with growth. (C) Internal Mg2 concentration could be significant only in the presence of high external Ca2l concentrations. (d) The contribution of nitrate and phosphate to the internal osmoticum was negligible. The ratio of external (Ca21)/(Na`)2 concentration is crucial for growth. Ratios above 0.5 x 10' per millimolar gave maximal protection from adverse effects of NaCl. Growth capacity was found to be determined by the combination of (Ca2l)/(Na)2 ratio and the absolute external concentration of NaCl. However, a correlation between internal K' concentration and growth capacity seemed independent of external NaCI concentration.Salinity is a major problem in irrigated agriculture and its role in reducing the yield of many crops is well documented (23). Reduction of plant growth under salt stress is usually attributed to osmotic stress due to a lowering of external water potential (24), or to specific ions effect on metabolic processes in the cell (10). The two effects are not mutually exclusive. Thus, ion regulation and osmoregulation are subjects of intensive research into possible mechanisms of salt tolerance (24).Studies of ion uptake in whole plants are complicated, since they involve ion uptake into the roots, transport of ions among various organs, and finally their accumulation in the leaves. The overall effect of salinity on growth is due to any possible combination of these processes. In recent years cell cultures have served as a very useful tool in trying to elucidate mechanisms of salt tolerance operating at the cellular level. Ion uptake and ion accumulation occur in the same cell, and no long-distance transport of ions takes place. tions (2,3,8,13,(27)(28)(29). It is commonly accepted that competition exists between Na+ and K+ leading to a reduced level of internal K+ at high external NaCl concentrations. This phenomenon has been described in plants as well as in cultured cells. Detailed studies with cotton plants showed a reduced content of K4 in roots subjected to high NaCl concentrations and that K+/ Na4 selectivity is an important factor in salt tolerance of plants (15). Recently, Leigh and Wyn Jones (22) hypothesized that critical K4 concentration is correlated with growth of plant cells. Studies of cell cultures of tobacco (29), alfalfa (8), and Citrus aurantium (3) showed that a higher level of internal K4 could be correlated with a higher level of salt tolerance. However, this is no...

The purpose of this work was to study the effect of various NO−3/NH+4 ratios in the nutrient solution at various root temperatures on strawberry (Fragaria ananassa) plants. The results could lead to a suitable NO−3/NH+4 ratio of the fertilizer solution to be applied in field‐grown strawberry plants in different seasons on sandy soils.3 Strawberry plants were selected for uniformity and transferred individually to a 1 L container through which the nutrient solution was flushed at a rate of 1 L/h. The total N concentration was 7 me/L. Five ratios of NO−3/NH+4, 7/0, 5/2, 3.5/3.5, 2/5, and 0/7, respectively, were used, each at four root temperatures (10, 17, 25, and 32°C). Constant NO−3/NH+4 ratio, constant total nutrient concentration, and constant pH (6.2) were maintained for 8 weeks. There is a general decline in root growth with increasing root temperature when a single source of N is supplied. This decrease is followed with a decrease in the sugar concentration of the roots. At 32°C root temperature gradual increase in the NH+4 fraction in the nutrient solution is followed by gradual deterioration of the plants to a complete death at 100% NH+4. This death is related to the depletion of sugars and possible shortage of oxygen in the root cells due to NH+4 metabolism in the root.

Strawberry plants (Fragaria ananasa Duch.) have shallow roots and are grown in the field during both hot and cold seasons. The possibility of irrigating and fertilizing the plants daily, through the trickle system, led to the question of what is the best nitrogen form and N03 /NHt ratios to be supplied to this crop during the growing season. The effect of four root temperatures (10, 17, 25 and 32 oq and five N03 /NHt mole ratios (0/7, 2/5, 3.5/3.5, 5/2, 7 /0) at constant total N in the solution was studied. To keep constant pH, total nutrient solution and root temperature, continuous flow techniques were used. The solution was flushed through 1-L pots at the rate of 1 L h-1 • When both N forms were present, the rate oftotal N uptake was higher than when NHt or NO) alone was present. The maximum uptake rate was found at 25 oc root temperature. Best conditions for growth were found at 25 oc root temperature when both N forms were present in equal concentration. A preference for NO) uptake was found during flowering and the fruiting period. Ammonium was preferred during the vegetative growth period. Increasing root temperature decreased total cation concentration and especially that of K+, Na+, and Mg 1 +, and increased Ca 1 + in the roots of NO) -fed plants. The Na + was accumulated in the crown and did not move to the leaves and fruits. Increasing root temperature reduced inorganic anion concentration in the roots while increasing it in leaves of NHt fed plants. In the fruits, the ratio of mole of charges of Cal+ to that of H 1 PO.;-was about 1:1 for both N forms.

The possibility of supplying nutrients daily to tomato plants (Lycopersicum esculentum Mill.) grown in various seasons raised the question of the best percentage NO3‐/ NH4+ to be supplied to these plants. The effect of four (8, 16, 24, and 34 C) temperatures and four percentage NO3‐/NH4+ (100/0, 75/25, 50/50, and 0/100) on the nutrient composition of tomato plants were studied. To obtain constant pH, percentage NO3‐/NH4+ and temperature continuous flow technique was used. The solution was flushed through the pots at a rate of 1 liter/hour. Increasing root temperature increased total‐N, P, Mg, and K in the shoot irrespective of percentage NO3‐/ NH4+ in the solution. Calcium concentration increased in the shoot with increasing temperature only when the plants were fed with NO3‐ as the only source of N. The presence of NH4+> in the nutrient solution caused a decrease in Ca concentration in tomato plants grown in temperatures 16 C and above. Increase in the root temperature increased total‐N and Ca, slightly increased P, and decreased Mg and K. Increasing root temperature increased N‐N03‐ concentration in the shoot, while decreasing it in thc roots. Low root temperature caused accumulation of N‐NO3‐ and K in the roots. It is suggested that the hindering of translocation of these ions at low temperature is one of the factors that slows down growth of tomato plants fed with nutrient solution containing a high ratio of NO3‐.

The increased use of combined irrigastion and fertilization under field conditions, and the possibility of sup plying nutrients to the plants daily raised the problem of the best percentages NO3‐/NH4+ to be supplied to tomato plants (Lycopersicum esculentum Mill) grown in the field in the various seasons. The objectives of this work were to find the most suitable percentages of NO3‐/NH4+ at various root temperatures, on growth and morphology of tomato roots. Tomato plants were grown in an experiment with a factorial design of four temperatures (8, 16, 24, and 34 C) and four percentages NO3‐/NH4+ (100/0, 75/25, 50/50, and 0/100) at constant N concentration of 10 meq/liter and constant pH of 6.5. To maintain the percentage NO3‐/NH4+ and pH constant, the nutrient solution was flushed through the pots at a rate of 1 liter per hour. When constant pH and constant solution composition were maintained the 50/50 NO3‐/NH4+ treatment showed the most growth, averaged over all temperatures. High percentage NO3‐/NH4+ retarded plant growth at low root temperatures but is preferred at high root temperature. Plants grown in solution rich in NO3‐ developed long, thin branched roots and those grown in solution rich in NH4+ developed short, thick second and third order roots. The results of this work can be directly applied to hydroponic systems and with a future field study it may produce new fertilizer solution compositions to be adapted to specific soil environmental conditions.