A shortened anthesis‐to‐silking interval (ASI) in maize (Zea mays L.) is associated with tolerance of stresses which occur around flowering. It is not known if this reflects differences in tassel and ear initiation dates, or in rates of development and growth. We examined these characteristics in selection cycles 0, 2, 4, 6, and 8 (designated Cx, where the subscript indicates the cycle number) of the lowland tropical maize population ‘Tuxpeño Sequía’, which was selected recurrently for drought tolerance and whose selection cycles differ for ASL Plants were grown at high plant density and under mild and severe drought stresses that occurred at flowering. Silking was delayed significantly, especially in C0 and C2 under severe drought. Stress treatments did not affect days to 50% tassel initiation, ear initiation, or anthesis. The interval between 50% tassel and ear initiation, the rate of spikelet initiation, and crop growth rate near flowering were unaffected by selection. Per cycle changes were −0.21 d in duration of ear spikelet initiation and −16.9 for spikelet number per ear at 50% anthesis. Selection changed relative growth rates at 50% anthesis by 0.005 d−1 cycle−1 for ears, 0.007 d−1 cycle−1 for spikelets and −0.009 d−1 cycle−1 for tassels. These changes were unaffected by stress level. Eight cycles of selection increased the mean ear and spikelet weights at 50% anthesis by 127 and 173%. The ASI increased rapidly when mean spikelet biomass at 50% anthesis was less than 0.8 rag. Results indicate that a decreased ASI arising from selection in this population is due largely to an increased rate of biomass accumulation per spikelet, and development of fewer spikelets per ear.

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Stem bromelain (EC 3.4.22.32) is a major cysteine proteinase, isolated from pineapple ( Ananas comosus) stem. Its main medicinal use is recognized as digestive, in vaccine formulation, antitumoral and skin debrider for the treatment of burns. To verify the identity of the principle in stem fractions responsible for the antitumoral effect, we isolated bromelain to probe its pharmacological effects. The isolated bromelain was obtained from stems of adult pineapple plants by buffered aqueous extraction and cationic chromatography. The homogeneity of bromelain was confirmed by reverse phase HPLC, SDS-PAGE and N-terminal sequencing. The in vivo antitumoral/antileukemic activity was evaluated using the following panel of tumor lines: P-388 leukemia, sarcoma (S-37), Ehrlich ascitic tumor (EAT), Lewis lung carcinoma (LLC), MB-F10 melanoma and ADC-755 mammary adenocarcinoma. Intraperitoneal administration of bromelain (1, 12.5, 25 mg/kg), began 24 h after tumor cell inoculation in experiments in which 5-fluorouracil (5-FU, 20 mg/kg) was used as positive control. The antitumoral activity was assessed by the survival increase (% survival index) following various treatments. With the exception of MB-F10 melanoma, all other tumor-bearing animals had a significantly increased survival index after bromelain treatment. The largest increase ( approximately 318 %) was attained in mice bearing EAT ascites and receiving 12.5 mg/kg of bromelain. This antitumoral effect was superior to that of 5-FU, whose survival index was approximately 263 %, relative to the untreated control. Bromelain significantly reduced the number of lung metastasis induced by LLC transplantation, as observed with 5-FU. The antitumoral activity of bromelain against S-37 and EAT, which are tumor models sensitive to immune system mediators, and the unchanged tumor progression in the metastatic model suggests that the antimetastatic action results from a mechanism independent of the primary antitumoral effect.

SummaryInterploidy crosses in flowering plants often cause seed abortion. Studies in maize have shown that failure of kernel development results from dosage effects among products of imprinted but as-yet-unknown genes in the endosperm, and that the operative stoichiometry is established for a ratio of two maternal genomes to one paternal genome. In this study, we used flow cytometry to monitor cell cycle activities in developing endosperms obtained after reciprocal crosses between diploid and tetraploid maize individuals. Our data show that dosage effects alter critical events involved in the establishment of endoreduplication during maize endosperm development. Particularly, maternal genomic excess (4x  2x crosses) forces endosperm cells to enter early into endoreduplication while paternal genomic excess (2x  4x crosses) prevents its establishment. Our results also suggest that altering mechanisms depend on two different sets of cell cycle regulatory genes -one imprinted through the female that is required for mitotic arrest, and another responsible for re-entry into S phase that is imprinted through the male. Further, molecular and physiological analyses should provide insights into the interaction of parental imprinting action and cell cycle regulation during endosperm development.

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