Stimulation Of Leaf Growth Research Articles

Leaf turnover and herbivory in the tall tussock grass Festuca orthophylla in the Andean Altiplano

Tall grass tussocks dominate the Andean highlands above 3,800 m a.s.l., with often no other life form contributing significantly to standing crop biomass and productivity, thus, representing the dominant source of fodder for camelid grazing. To assess the productivity of these semi-arid tropical rangelands (350 mm of annual rainfall confined to a 4–5 months rainy season) is challenging, given the ‘evergreen’ nature of leaves and the unknown periodicity of leaf growth. The aim of this study was to explore the seasonal course of new foliage formation, foliage duration, and the response of leaf elongation and emergence to simulated llama grazing (clipping). The repeated census of Festuca orthophylla leaves in the Sajama National Park at 4,250 m elevation (Bolivia) provided clear evidence that leaf production is not confined to the rainy season, but also occurs during the dry season. Our data revealed a mean leaf longevity of 141 days for peripheral control tillers (unclipped) and 169 days for central control tillers. Leaves grow slower and reach shorter length during the dry season compared to the rainy season, and peripheral tillers are always shorter but more vigorous than central tillers (shorter intervals between the emergence of two leaves). There was no stimulation of leaf growth in tillers that were clipped (no overcompensation). Overall, this study suggests ca. two-fold replacement of foliage per year. We explain the continued growth in the dry season by, on average, six times greater soil area occupied by roots than by the leaf canopy, and thus, much greater water availability per tussock than meteorological data would suggest. Wide spacing of tussocks and a large root-sphere mitigate the impact of periodic drought on tissue formation, providing year-round forage for llamas.

Changes in organ growth ofChenopodium rubrum due to suboptimal and multiple photoperiodic cycles with and without flowering effect

The growth changes of cotyledons, leaves, hypocotyls and roots due to photoperiodic induction in short day plantChenopodium rubrum were investigated in relation to flowering. Six-day old plants were induced by photoperiods with a different number of dark hours. We found that the degree of inhibition which occurred during induction in the growth of leaves, cotyledons and roots similarly as the stimulation of hypocotyl is proportional to the length of dark period. The photoperiods with 12, 16 and 20 dark hours bring about marked inhibition of growth and at the same time induce flowering in terminal and axillary meristems. The inhibitory effect of critical period for flowering,i.e. 8 dark hours, is not apparent in all criteria used and even the flower differentiation is retarded. The photoperiods of 4 and 6 dark hours did not affect growth and were ineffective in inducing flowering even if their number has been increased. The experiments with inductive photoperiod interrupted by light break have clearly shown that growth pattern characteristic for induced plants can be evoked in purely vegetative ones. Such statement did not exclude the possible importance of growth inhibition as a modifying factor of flower differentiation. We demonstrated that the early events of flower bud differentiation are accompanied by stimulation of leaf growth. The evaluation of growth and development of axillary buds at different nodes of insertion enabled us to quantify the photoperiodic effect and to detect the effects due to differences in dark period length not exceeding 2 hours.

Cytokinin‐like Activities of 4‐Benzylaminobenzimidazole

AbstractA new compound, 4‐benzylaminobenzimidazole was synthesized. The only difference between benzylaminobenzimidazole and benzylaminopurine is the presence in the former of carbon atoms instead of the nitrogen at positions 1 and 3 of the purine ring. Although the new compound has no purine ring in the molecule, it has several cytokinin activities such as stimulation of leaf growth in Raphanus and retention of chlorophyll in Brassica leaves. Benzylaminobenzimidazole has no effect on germination of tobacco seeds kept in the dark.