Yosef Mizrahi

Modified CTAB Procedure for DNA Isolation from Epiphytic Cacti of the Genera Hylocereus and Selenicereus (Cactaceae)

We present a simple protocol for DNA isolation from climbing cacti, genera Hylocereus and Selenicereus. The abundant polysaccharides present in Hylocereus and Selenicereus species interfere with DNA isolation, and DNA extracts, rich in polysaccharides, are poor templates for amplification using polymerase chain reaction (PCR). We used roots as the source tissue due to the lower viscosity of the extracts relative to that of other tissues. The extraction and isolation procedure we devised consists of the following steps: (1) three washes of ground tissue with the extraction buffer to remove the polysaccharides; (2) extraction with high-salt (4 M NaCl) cetyltrimethylammonium bromide (CTAB) buffer to remove the remaining polysaccharides; (3) removal of RNA by RNase; (4) phenol:chloroform extraction to remove proteins; (5) chloroform extraction to remove remaining phenols. The yields ranged from 10 to 20 μg DNA/g fresh roots. DNA samples prepared by our method were consistently amplifiable in the RAPD reaction and gave reproducible profiles.

Ornithine decarboxylase activity in rapidly proliferating plant cells

Polyamines are widely distributed in nature, but their precise role in cellular processes is not fully understood. Polyamines are associated with cell proliferation, tissue regeneration and malignancy [l-3]. Most of the information on the biosynthetic pathways of putrescine, spermlne and spermidine, their regulation and possible sites of action has been obtained from studies with micro-organisms or mammalian cells. In mammalian cells, putrescine is synthesized from Lornithine by Lornithine decarboxylase (ODC EC 4.11.17) [2]. In plants, however, it is commonly accepted that putrescine is formed from Larginine by Larginine decarboxylase (ADC EC 4.11.19), via the intermediate agmatine. The activity of ODC in plants is usually found to be much lower than that of ADC [4-71, and ODC has therefore been claimed to be of little significance in the formation of putrescine in plants. We felt that in plant cells such an essential biosynthetic pathway of putrescine should not differ from that in mammalian cells and therefore decided to study ODC activity in plant systems. We chose to search for ODC activity in two plant systems of rapidly proliferating cells the XD cell line of tobacco in suspension culture and tomato ovaries before and after pollination. After subculture of XD cells there is usually a lag period of a few days, after which the culture enters an exponential phase, lasting for several generations [8]. The culture then enters a stationary phase. In tomato ovaries before pollination there is some cell division; after pollination there is very intense cell division, which lasts for

Ripening behaviour and responses to propylene in four cultivars of Japanese type plums

Abstract The aim of this study was to determine the physicochemical changes in highly coloured cultivars of plums that could be used as a guide to assessing optimum harvest maturity. The patterns of fruit growth and maturation were investigated in the cultivars: Gulfruby, Beauty, Shiro and Rubyred. Changes in the rates of respiration and ethylene production, skin colour, firmness, soluble solids concentration and titratable acidity were recorded at intervals from pit-hardening until the fruit were tree ripe. In order to evaluate the role of ethylene in the ripening process, propylene was applied to harvested fruit. Internal ethylene concentrations in the cv. Rubyred were also measured at intervals after pit-hardening either in harvested fruit or fruit attached to the tree. Studies of the changes in the physiological parameters associated with ripening showed that none were suitable for the assessment of harvest maturity in all cultivars of plums. However, this analysis revealed two distinct patterns of ripening behaviour in the cultivars studied. Gulfruby and Beauty showed a typical climacteric pattern of development, whilst Shiro and Rubyred exhibited a suppressed-climacteric phenotype. This phenotype appears to result from an inability of the fruit to produce sufficient quantities of ethylene to co-ordinate ripening. However, treatment with propylene showed that fruit displaying the suppressed-climacteric phenotype should still be placed in the climacteric class. This suppressed-climacteric character could be incorporated into plum breeding programs to produce new varieties with improved storage properties.

Ripening and postharvest behaviour of fruits of two Hylocereus species (Cactaceae)

Abstract Fruit growth and ripening, and the effect on fruit quality of various storage temperatures, were studied with Hylocereus undatus and Hylocereus polyrhizus plants growing in Beer-Sheva (Israeli Negev desert) under greenhouse conditions. Fruit growth was sigmoidal with a strong decline in growth rate after the onset of peel colour change. The first change in peel colour was recorded 24–25 days after anthesis in H. undatus and 26–27 days in H. polyrhizus . In both species, the peel turned fully red 4–5 days after the first colour change (mean temperature for the study period was 26.6±2.1°C). The slow growth phase was characterised by a decrease in the proportion of peel and concomitant increase in that of pulp, increase in the concentration of soluble solids and soluble sugars and a decline in firmness and the concentration of starch and mucilage. The surge in acidity prior to colour change indicated the beginning of the ripening processes. For H. polyrhizus , which has a red–violet pulp, the increase in pulp pigment paralleled the development of peel colour. Fruits were non-climacteric, and when harvested at close to full colour, they retained market quality for at least 2 weeks at 14°C or 1 week at 20°C. Storage at 6°C is not recommended, because transfer from that temperature to room conditions caused fruits to lose their firmness and flavour rapidly.

Cytology and mating systems in the climbing cacti Hylocereus and Selenicereus

Chromosome numbers and meiotic behavior are reported for the climbing cacti species Hylocereus undatus, Hylocereus polyrhizus, and Selenicereus megalanthus. The Hylocereus spp. are diploid (2n = 22), while S. megalanthus is a tetraploid (2n = 44). Irregular chromosome disjunction at anaphase I in pollen mother cells of S. megalanthus is probably the major cause of its reduced pollen viability and may contribute to low seed set, low number of viable seeds and, consequently, low fruit mass. A pollination study confirmed self-incompatibility in H. polyrhizus and a weakened incompatibility reaction in H. undatus and S. megalanthus. Major crossability barriers do not exist between the Hylocereus spp. investigated. Reciprocal intergeneric crosses were successful between Hylocereus spp. and S. megalanthus, suggesting that an Hylocereus sp. might be one of the diploid progenitors of the tetraploid S. megalanthus. The implications of the results on cacti nomenclature and systematics are briefly discussed.

Responses of two hemiepiphytic fruit crop cacti to different degrees of shade

Selenicereus megalanthus and Hylocereus polyrhizus, hemiepiphytic cacti of shady habitats, have recently been introduced as fruit crops to the Negev Desert of Israel. Since they become bleached and die when they are grown in full sunlight, the shading responses of these cacti were studied. Both species showed typical CAM CO2 fixation, namely CO2 was fixed during the night, followed by acid accumulation. Nocturnal acid accumulation and the concentration of photosynthetic pigments (chlorophyll and carotenoids) were determined in short term experiments in the summer under full sunlight or in net houses with 30, 60 or 90% shade. The effect of shading on morphological traits, growth and fruiting was determined in long term experiments, in net-houses only, since plants usually degenerate under full sunlight. S. megalanthus was found to be more sensitive to high light flux density and better adapted to deep shade than H. polyrhizus, as judged from the more marked decrease in both nocturnal acid accumulation and in the concentrations of chlorophyll and carotenoids under full sunlight in the former species. In addition, under 90% shade the stem biomass of S. megalanthus was reduced less than that of H. polyrhizus. In response to the shade, stem ribs became shallow, root dry weight decreased and shoot water content increased in both species. The most favorable conditions for growth and fruit production were found to be 30% shade for H. polyrhizus while for S. megalanthus 60% shade seemed to be preferable, since it facilitated higher acid accumulation, carotenoid and chlorophyll content, and better stem appearance. H. polyrhizus was distinguished by its higher fruit yield, estimated at 16 ton ha−1 vs. 3.8 ton ha−1 for S. megalanthus in the second year after planting when both species were growing under optimal conditions. The differences between the species in terms of light adaptation may be partially related to the wax layer coating the stem and sunken stomata of H. polyrhizus compared to S. megalanthus, which had neither wax nor sunken stomata.

Effect of salinity on quality of various agricultural crops

The effect of salinity on the quality of various agricultural crops has not yet been explored much. This information is very important to Israel due to the increasing use of saline water for irrigation. This paper reports the effect of saline irrigation water on the quality, especially the taste, of several crops. Fruits from a processing tomato cultivar exposed to various degrees of salinity had higher values for total soluble solids (TSS) and acidity than their controls. The yield of fruit after saline water irrigation is lower, but this is offset by the higher fruit quality and its consequent higher value. Melon fruits from plants subjected to saline water scored higher in taste than their controls when the fruits were analyzed fresh. After 3–4 weeks of storage at room temperature, there was no longer any difference in taste. Even though salinity slightly increased the TSS content, this did not correlate with the taste scores. Iceberg lettuce grown with saline water did not significantly differ in taste from its control, even when the sensitive triangle taste test was used. The same was true for peanuts. Thus, for these two crops no advantage of better quality would compensate for possible lower yields. Salinity had little effect on the yield of two varieties of Chinese cabbage, but increased the frequency of tipburn.

Organogenesis in the vine cactus Selenicereus megalanthus using thidiazuron

Segments of distal and proximal parts of the cotyledons, hypocotyls and epicotyls of yellow pitaya [Selenicereus megalanthus (Cactaceae)], were cultured on Murashige and Skoog (MS) medium supplemented with thidiazuron (TDZ). The proximal part of the cotyledons was found to be the most responsive tissue, maximal bud regeneration being achieved in the presence of 200 μM thidiazuron. However, TDZ does not change the pattern of regeneration competence, which remains restricted to the proximal part of the cotyledons. The best medium for shoot elongation was found to be MS lacking plant growth regulators. Rooting was induced on MS medium supplemented with 5.3 μM naphthaleneacetic acid. Rooted plantlets were transferred to a soil medium and acclimatized successfully in a greenhouse.

Growth and oil production of argan in the Negev Desert of Israel

Abstract Argan (Argania spinosa L.) is a wild tree native to southwestern Morocco. It bears a plum-sized fruit with one to three kernels rich in oil. The oil is highly prized as an edible and cooking oil by the local people. Our study was carried out to investigate the possibility of domesticating the species. Seedlings were planted in the Negev Desert of Israel at the location Qetura with a high summer temperature and brackish water and at the location Ramat Negev with a low winter temperature and good-quality water. Average tree height in the seventh year was 4.0±0.6 m at Qetura and 4.6±0.6 m at Ramat Negev. Best yielders produced dry fruits between 20 and 25 kg/tree at both sites in the sixth and seventh years, and average orchard yield was three-four-times lower as a result of high variation between the trees. Kernels comprised 6.5% of fruit weight and contained 55% of oil. In the seventh year, oil yield was 0.6 kg/tree at Qetura and 50% lower at Ramat Negev. The higher oil yield at Qetura is related to higher average fruit yields, higher kernel weights and higher oil content of the kernels than the values for Ramat Negev. Characteristics of the fruits and fatty acid composition of the argan oil and the chemical composition and quality characteristics of the defatted argan kernel meal are being presented. Fruit components, such as the pericarp (45% of fruit weight), and the defatted meal (3.5% of fruit weight) can be used as animal feeds. The meal is characterized by a high protein content (46%) and a high in vitro digestibility (96%).

The effect of ripening stage on fruit quality after storage of yellow pitaya

Abstract Some physicochemical properties and flavour quality were determined in yellow pitaya ( Selenicereus megalanthus ) fruits harvested either at the beginning of ripening (colour break), or when they reached good eating quality (advanced colour stage), and then stored for up to 4 weeks at either 10 or 20°C. Colour-break fruits stored at 10°C ripened only after being transferred to 20°C. During ripening such fruits attained the physical properties of fruits ripened on the plant, but they contained significantly lower concentrations of soluble sugars and acidity, and had an inferior taste. Fruits harvested at the advanced colour stage and stored at 10 or at 20°C were also inferior to those of freshly-harvested fruits with respect to soluble sugars and acidity as well as taste quality, but their physical properties changed only slightly during storage. In both groups of fruit water was translocated from the peel to the pulp during storage. The lower weight loss, higher soluble sugar concentrations, and lower susceptibility to pathogens of advanced colour fruits as compared with colour-break fruits, suggest that the former stage is the correct one for harvest.