Aliza Benzioni

Water Stress and Hormonal Response

A transient water deficit is a frequent and recurrent phenomenon experienced by most plants. Hence it can be assumed that efficient adaptive mechanisms were developed in the course of evolution which enable plants to cope with water deficits of varying intensities. Evidence is accumulating that these adaptive mechanisms whether rapid, like stomatal movement, or slow, like developmental and morphological adaptation, may involve regulation through changes in the hormone balance of the plant (Hsiao, 1973; Livne and Vaadia, 1972). Plant response to environmental changes requires a complex control system. Even a very simple control system is necessarily made up of several components such as receptor, integrator, modulator, effector and amplifier, and growth regulators may logically be presumed to be part of such a system.

Effect of different salts and of ABA on growth and mineral uptake in Jojoba shoots grown in vitro

Summary ABA and different kinds of salinity were compared for their effect on shoot development in salt-sensitive and salt-tolerant jojoba clones. Shoot segments were proliferated in vitro in the presence of different salts or different concentrations of ABA. Growth parameters (shoot elongation, new node production, dry weight, leaf length) and accumulation of Na + , K + , Ca 2+ , Cl − , and SO 4 2- were examined. Wax deposition on leaves was detected by electron scan microscopy. Chloride salinity reduced shoot elongation, node production, and biomass production in salt-sensitive clones, while in salt-tolerant clones its adverse effects were generally less pronounced (although significant inhibition was observed in the presence of Na 2 SO 4 ) or it even enhanced growth. The effect of ABA on shoot growth was similar to that of the chloride salinities, with salt-sensitive clones responding to much lower ABA concentrations than the salt-tolerant ones. Unlike ABA, salinity (mainly salts containing Cl − anions) significantly promoted leaf expansion in both sensitive and tolerant clones. ABA and salinity induced some epicuticular wax deposition on leaves of salt-sensitive clones. The conclusion is that the salt sensitivity of jojoba clones is partly related to sensitivity to ABA.

Effect of NaCl Salinity on Growth and Development of Jojoba Clones: 11. Nodal Segments Grown in Vitro

Summary In an effort to determine the degree of correlation between effects of salinity in vitro and in vivo, the response of nodal segments of jojoba (Simmondsia chinensis) was studied in four superior clones under salinities of 0-274 mM NaCl and in a mixed group of clones under 171 mM NaCl. In general, NaCI up to 137 mM did not markedly inhibit rate of shoot elongation, biomass and node production in superior clones 106, 104, and 154, but higher levels distinctly inhibited growth. Growth of clone 64, one of the superior clones, showed inhibition at all salinity levels. Clone 154 was the most tolerant of the four up to 205 mM NaCl. Sodium accumulation was highest in shoots of clone 64 and lowest in clone 154. Potassium content decreased progressively with salinity in all but clone 154, in which no change in potassium content occurred. The response of other clones of the mixed group to 171 mM NaCl was highly variable, some exhibiting 70-80% inhibition in shoot elongation as compared with the control, and others remaining largely unaffected even when sodium accumulated to high levels. When these results were compared with findings of the preceding ex vitro study, it was found that in spite of anatomical and physiological differences, the response to salinity of nodal segments in vitro and that of the whole plant in vivo was similar, supporting the idea that in vitro screening of organs offers an efficient, inexpensive method of preselecting for salt tolerance.

The importance of pH in food selection by the tobacco whitefly,Bemisia tabaci

The tobacco whitefly,Bemisia tabaci Gennadius, was found to differentiate between pH values at the leyel of 0.25. It had a clear preference for media with pH values of 6.0 to 7.25 offeredin vitro, in both choice and no-choice situations, when “resting whiteflies” or survival was measured. The whiteflies showed a clear preference for a sucrose concentration of 15%. The addition of 10% sucrose to buffers at various pH values did not change the pattern of their pH preference. Inin vivo experiments whiteflies preferred old cotton leaves (120 days) to younger leaves (60 days). The pH of old leaves was 6.8 while that of young leaves was 5.9. These results may explain the fact that whiteflies attacked cotton plants in commercial fields only late in the season, when the pH values of the cotton leaves exceeded pH 6.

IMPROVEMENT OF JOJOBA SHOOT MULTIPLICATION IN VITRO BY VENTILATION

SummaryThe effect of ventilation during the multiplication stage on the development of propagules from different clones of jojoba [Simmondsia chinensis (Link) Schneider] was investigated. Variation in the response to ventilation was due to genotype, the extent of ventilation, and to the period of exposure (transfer number). With intermediate ventilation treatments, propagules elongated to a greater extent and produced more dry biomass than propagules grown without ventilation. In the highest ventilation treatment, however, growth parameters were negatively affected. More importantly, propagules grown with moderate ventilation produced more plant material suitable for further multiplication and for the elongation stage than those grown in sealed tubes—the vessels used in our original micropropagation system. In five of the seven clones studied, growth and multiplication rate were decreased by the highest ventilation treatment. Propagules from the second and third multiplication transfers into ventilated vessels became more sensitive to high ventilation. Ambient water loss was slower in propagules produced under ventilation, probably due to smaller stomatal apertures. As a result of improved growth and decreased hyperhydricity by ventilation, the micropropagation protocol should be modified to include Magenta boxes equipped with vented lids as the preferred growing vessels.

Yield parameters in young jojoba plants and their relation to actual yield in later years

Abstract A total of 30 jojoba clones, among them six already commercial clones and 24 newly selected ones were characterized in terms of yield parameters, chilling requirements and morphological traits. The aim was to supply farmers (from Israel and abroad) better yielding clones. Considerable variability was found among the clones in all the parameters. Some clones exhibited excellent vegetative traits related to yield potential, such as a high survival rate, rapid growth, extensive branching, high node density, while others exhibited outstanding reproductive traits, such as earliness, high flower density, high percentage of fruit set, high seed weight, and high wax content in the seed. The clones also differed in their wax composition. Plants began to yield 2 years after planting in the field, some having commercial yields as early as their third year. The best clones with respect to wax yield were Hazerim, Negev, BGU, Forti, and Gvati, all new clones not yet planted in commercial plantations. An attempt to relate yield parameters at the third year to wax yield at their sixth year was made. The height in the third year and the flower index, relative fruit set and seed weight were related to yield. The flowering pattern of all clones was followed up during the season 1993/94, which was characterized by a combination of cool night temperatures with warm days. This weather enabled the clones that broke dormancy to flower during the winter instead of spring. We were thus able to identify clones with different chilling requirement. In conclusion some very promising clones with high yields can be added to our commercial clones. Owing to the new information gathered on depth of dormancy and flowering pattern, clones can also be allocated to environments differing in climatic conditions.

Long-term effect of irrigation with saline water on the development and productivity of jojoba clones

SummaryThree commercial clones of jojoba (Simmondsia chinensis) (64, Q-106 and 879–154) were planted in June 1991 at the Ramat Negev Experimental Station (Israel) and fertigated with water at three salinity levels, 1.2, 3.4 or 6.2 dS m−1. The effects of salinity over three and a half years on key metabolic activities, on plant growth and development, on flowering characteristics, and on yield were studied. Salinity barely inhibited the rate of net photosynthesis, although it did reduce stomatal conductivity by about 50%. Salinity also affected the water status of the plants by reducing water potential. Growth of the plants was not greatly affected by salinity. It was found that jojoba plants accumulate sodium and chloride ions in their leaves and use a strategy typical of many halophytes to cope with the salinity. The effect of salinity on flower development was also studied, since the vitality of flowers is a key factor in obtaining seeds. Salinity did not affect the timing of the breaking of flower bud ...

Genetic variation in pigeon pea (Cajanus cajan (L.) Mill sp.) in response to successive cycles of water stress

Four pigeon pea [Cajanus cajan (L.) Mill sp.] cultivars were studied during two cycles of development of water stress and recovery. During these two cycles the genetic variation in vegetative development, leaf water potential, relative water content, photosynthesis, and stomatal conductance was followed. Plants were grown in a greenhouse and irrigated every seventh day. On two occasions (30 days and 80 days from sowing) water was withheld for 13 days in one group of plants and 16 days in another. Control plants were irrigated as usual. The four cultivars differed in their response to drought, with ICPL 215 being the most tolerant cultivar. In the plants exposed to the 13-day water stress, the first stress cycle resulted in preconditioning of plants such that higher values for carbon dioxide exchange rate and relative water content were observed in the second stress cycle. The longer stress period (16 days) resulted in some damage to the photosynthetic capacity and in a slow recovery rate in both cycles. During the second drought cycle the plants retained a water content above the critical value, possibly due to osmotic adjustment. It seems that water status parameters, especially relative water content, may serve as indicators of drought tolerance in pigeon pea varieties and may be useful in breeding programs for cultivation of pigeon pea under semiarid conditions.

Pollen production and pollen viability in male jojoba plants

Jojoba (Simmondsia chinensis (Link) Schneider) is a dioecious wind pollinated shrub native to the Sonora desert of the southwestern USA and Northern Mexico. A comprehensive program for the selection of female cultivars was conducted in Israel for many years. However, selection for male cultivars as pollen sources has largely been neglected. The current use of male seedlings with their large variation in bloom period, amount of pollen produced, and pollen viability, could result in insufficient pollination and reduced yields. The study was conducted at Hazerim plantation, Israel (northern Negev desert), on 8–9-year-old male jojoba plants. Pollen production was investigated 24 and 48 h after removal from the plants. Pollen viability was tested both in vitro and in vivo. Pollen production, in percent pollen from inflorescence fresh weight, was the highest during peak male bloom. The greatest amount of pollen having the best germinability was collected 24 h after the inflorescences were removed from the plants. In vitro germinability of jojoba pollen was affected by pollen source, and by sucrose concentration of the germination solution. Jojoba pollen from all pollen sources germinated intensively on the stigmas of the female flowers, but the percentage fruit set was different for various pollen donors. Several male plants from our study showed promising traits as potential male cultivars in terms of pollen production and viability.

Absorption and distribution of orally administered jojoba wax in mice

The liquid wax obtained from the seeds of the arid-land shrub jojoba (Simmondsia chinensis) is finding increasing use in skin treatment preparations. The fate of this wax upon reaching the digestive tract was studied.14C-Labeled wax was administered intragastrically to mice, and the distribution of the label in the body was determined as a function of time. Most of the wax was excreted, but a small amount was absorbed, as was indicated by the distribution of label in the internal organs and the epididymal fat. The label was incorporated into the body lipids and was found to diminish with time.Lipids 17: 169–171. 1982.