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Determination of profiles and total contents of betacyanins in cactus fruits of Hylocereus species using chromatographic and spectrophotometric method is described. The investigated species were H. polyrhizus, H. purpusii, H. costaricensis, H. sp. 487 (all red-flesh species and hybrids made among them), and the white- or red-flesh species H. undatus. Hybrids included hybrid 1 (H. undatus white-flesh clone and H. sp. 487), hybrid 35 (H. sp. 487 and H. polyrhizus), and the reciprocal hybrid hybrid 95 (H. polyrhizus and H. sp. 487). Fruits of H. polyrhizus exhibited the highest relative concentration (expressed as percentage of the total HPLC peak area) of hylocerenin, a recently discovered pigment, and a high relative concentration of phyllocactin. Hylocerenin and isohylocerenin, present in fruits at relative concentrations of 11.7 and 5.8%, respectively, are probably responsible for the fluorescent color of the fruit pulp. H. costaricensis fruits have a much higher content of phyllocactin (63.9%), which is almost 4 times higher than the betanin content. These differences in pigment concentrations might explain the differences in red hues of the flesh of these fruits.

The reproductive biology of the climbing cacti Hylocereus polyrhizus (Weber) Britt. & Rose, H. undatus (Haworth) Britt. & Rose, H. costaricensis (Weber) Britt. & Rose, and Selenicereus megalanthus (Schum. ex Vaupel) Moran (syn. Mediocactus megalanthus) was studied with the aim of cultivating the cacti in Israel as fruit crops. Flowering in Hylocereus spp. occurred in two to three waves during the summer, whereas in S. megalanthus, flowering was concentrated at the end of autumn. Flowers of all species opened 1 to 1.5 hours before sunset and closed ≈6 hours after sunrise. In the Hylocereus spp., H. polyrhizus and H. costaricensis were self-unfruitful, and cross-pollination with other species led to high fruit set (100%). Hylocereus undatus was self-fruitful, setting fruit with self-pollen. Cross-pollination between the clones of S. megalanthus led to a high fruit set and each clone was self-fruitful. In contrast to H. undatus, S. megalanthus clones could set fruit without pollen vector involvement, although the set was slightly lower than with hand pollination. Pollen source influenced fruit weight. In the self-fruitful species of Hylocereus, fruit obtained by hand cross-pollination with other Hylocereus spp. were significantly heavier than fruit obtained by hand self-pollination. The largest fruit in each of the Hylocereus spp. were obtained by specific cross-combinations within the group. Fruit of S. megalanthus had a lower weight than fruit of the Hylocereus spp. Flowers of all species were visited by day-active honeybees only. Fruit set and fruit weight with open pollination was lower than with hand pollination in Hylocereus spp. Since stigma receptivity and pollen germinability stayed high during anthesis, the low pollination effectivity has to be related to other factors, such as the short bee visits and the absence of specific adaptation by the bees to the flower. In S. megalanthus, fruit set and fruit weight with open pollination were similar to values obtained with hand pollination. This similarity is probably related to the fact that pollen transfer in open pollination is achieved by bee visits and direct transfer of pollen to the stigma, which occurs via physical contact between anthers and stigma during flower closing.

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The apparent association of ornithine decarboxylase (ODC) with rapid cell proliferation in developing tomato (Lycopersicon esculentum Mil. cv.Pearson ms-35) fruits has been previously described. Further evidence is provided by the use of two ODC inhibitors, a-difluoromethylornithine (a-DFMO) and a-methylornithine (a-MO). Fruit development was inhibited by these inhibitors if applied during the period of intensive cell division. When applied in vitro, the two inhibitors were shown to inhibit the activity of ODC but not that of arginine decarboxylase (ADC). When applied in vivo, a-DFMO, a catalytic irreversible inhibitor, caused 97.1% reduction of ODC activity in the dialyzed extract from the treated ovaries, while it had no effect on ADC. On the other hand, a-MO, a reversible inhibitor, did not reduce the activity of these two enzymes in the dialyzed extracts when applied in vivo. The dialysis procedure probably removed a-MO from the enzyme fraction. Putrescine, the product of both ODC and ADC, aleviated the inhibition of fruit development but did not restore ODC activity to the control level. These results suggest that in the young developing tomato fruit, ODC is the enzyme responsible for the synthesis of putrescine, which is essential for the early stages of fruit development. The reduced activity of ODC elicited by putrescine suggests a mechanism of feedback regulation by enzyme repression or release of an ODC anti-enzyme.Polyamines are widely distributed in nature, but their precise role in cellular processes is not always fully understood. They are associated with cell proliferation, tissue regeneration, and malignancy (1,6,7,17,18). Most of the information on the biosynthetic pathways of putrescine, spermidine, and spermine, their regulation, and the possible site of action has been obtained from studies with microorganisms and mammalian cells (1). Such information is lacking for plant systems. Several reports (4,8,14,15,(20)(21)(22) do, however, describe the presence of various polyamines in plants and the occurrence of enzymes involved in polyamine biosynthesis, e.g. ODC3 and ADC. It is commonly accepted that ADC is the enzyme responsible for the production of putrescine in plants and that ODC is of lesser importance (14,15,(20)(21)(22)).We have recently described an apparent association between elevated ODC activity and rapid cell proliferation in two plant systems: tomato ovaries during the first 10 d after pollination and ' The work was performed in partial fulfillment of the requirements for the PhD thesis of E. C.'To whom correspondence should be addressed. 'Abbreviations: ODC, ornithine decarboxylase; ADC, arginine decarboxylase; a-DFMO, a-difluoromethylornithine; a-MO, a-methylornithine.tobacco XD cells growing in suspension culture during the logarithmic phase of growth (9). ADC was also present in tomato ovaries. However, its activity did not change during the logarithmic phase of growth, being one-fourth of this maximal level of ODC (E. Cohen, S. (Malis) Arad, Y. M. Heimer, and Y. Mizra...

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.