Protease activity, organisation of vegetative primordia and effect of putrescine in tobacco thin layers

Since in tobacco thin layers exogenous putrescine alters the physiological and mor-phogenic responses induced by IAA (indole-3-acetic acid) and/or BA (benzylade-nine), the effect of this polyamine on protease activity and on the formation of meristemoids and vegetative primordia was studied during morphogenesis. Superficial thin layer explants, excised from the stem of tobacco (Nicotiana tabacum L. cv. Samsun) plants in the vegetative stage, were cultured under various hormonal conditions (IAA, IAA+BA, BA) and in a hormone-free medium, in the presence or absence of 100 μM putrescine. Histological analysis showed that no meristemoids were formed on the control medium or with putrescine alone and only a few were formed on IAA-treated explants with or without putrescine. An increasing number of meristemoids was observed in IAA+BA and BA treatments during culture; in both cases this number was enhanced by the presence of exogenous putrescine. Protease activity was evaluated spectrophotometrically using two synthetic substrates, azocasein and N-benzoyl-DL-arginine-p-nitroanilide (BAPNA). In the former, maximum protease activity was observed in IAA+BA- and BA-treated explants on days 10 and 15, respectively, while with IAA activity was lowest, the maximum occurring on days 5–10. In this case exogenous putrescine enhanced protease activity in the presence of IAA alone or with BA, while it decreased it in the presence of BA. BAPNA-mediated proteolytic activity (serine-proteases) was highest in IAA+BA-treated explants, intermediate in BA- and not different from controls in IAA-treated explants. Putrescine only affected proteolytic activity in IAA+BA treatments. The use of specific inhibitors of protease activities indicated that these enzymes belong to two main classes of proteases, that is serine- and thiol-proteases. The pattern of proteolytic activities during culture appeared to be related to the differentiation of meristemoids into vegetative primordia. The effect of exogenous putrescine on protease activity was different depending on different synthetic substrates, developmental patterns, pH and ionic strength.     

Retinoic acid and mammalian craniofacial morphogenesis

Retinoic acid is a morphogenetic signalling molecule in vertebrate embryos, one being known to perform a specific function in organizing the body pattern along the anteroposterior axis. This molecule has especially attracted research attention because retinoic acid treatment will also induce abnormal morphogenesis, particularly in the craniofacial structures. The present review discusses recent molecular insights revealing how the retinoic acid signal is transduced within a cell, specifically focusing on the involvement of cranial neural crest cells in retinoic acid-induced abnormal morphogenesis in the mammalian head     

Plastid structure and chlorophyll content in leaf primordia of onion bulbs

Angiosperms do not synthesize chlorophyll in the dark. Here we show that leaf primordia in onion bulbs are green, though they developing in dark conditions. We present results that show plastids in green primordia are chloroplasts, and that they contain chlorophyll as well as embryos in seeds of certain angiosperms.     

<Emphasis Type="Italic">In vitro</Emphasis> rooting of microshoots of <Emphasis Type="Italic">Cotinus coggygria</Emphasis> Mill,a woody ornamental plant

Studies on rooting of microshoots of smokebush (Cotinus coggygria Mill, var. Royal Purple), a woody ornamental, were carried out in vitro. Microshoots were rooted in a mixed-auxin regime (indole 3-acetic acid, indole butyric acid [IBA], and naphthalene acetic acid) or singly in the above auxins and the 2,4 dichlorophenoxyacetic acid (2,4-D) over a wide concentration range. Indole butyric acid at 10 μM proved to be the most suitable treatment, producing less basal callus, 100% rooting, and earlier root emergence than the other treatments. No roots were formed with 2,4-D. A 6-day root induction period was obtained with 10 μM of IBA. Histological studies revealed increased mitotic activity after 3 d in culture in the medullary ray cells, which led to root primordium formation, several of which were formed simultaneously around the base of the explant. The vascular tissues of these primordia connected to those of the explant, and roots began to emerge from the base by day 10. Thus, direct rhizogenesis occurred with the IBA treatment, as opposed to the roots that were formed in the basal callus under the mixed-auxin regime.     

Life cycle stage and water depth affect flooding-induced adventitious root formation in the terrestrial species Solanum dulcamara

Background and Aims Flooding can occur at any stage of the life cycle of a plant, but often adaptive responses of plants are only studied at a single developmental stage. It may be anticipated that juvenile plants may respond differently from mature plants, as the amount of stored resources may differ and morphological changes can be constrained. Moreover, different water depths may require different strategies to cope with the flooding stress, the expression of which may also depend on developmental stage. This study investigated whether flooding-induced adventitious root formation and plant growth were affected by flooding depth in Solanum dulcamara plants at different developmental stages.Methods Juvenile plants without pre-formed adventitious root primordia and mature plants with primordia were subjected to shallow flooding or deep flooding for 5 weeks. Plant growth and the timing of adventitious root formation were monitored during the flooding treatments.Key Results Adventitious root formation in response to shallow flooding was significantly constrained in juvenile S. dulcamara plants compared with mature plants, and was delayed by deep flooding compared with shallow flooding. Complete submergence suppressed adventitious root formation until up to 2 weeks after shoots restored contact with the atmosphere. Independent of developmental stage, a strong positive correlation was found between adventitious root formation and total biomass accumulation during shallow flooding.Conclusions The potential to deploy an escape strategy (i.e. adventitious root formation) may change throughout a plant’s life cycle, and is largely dependent on flooding depth. Adaptive responses at a given stage of the life cycle thus do not necessarily predict how the plant responds to flooding in another growth stage. As variation in adventitious root formation also correlates with finally attained biomass, this variation may form the basis for variation in resistance to shallow flooding among plants.     

The prediction of leaf canopy expansion in the leek from a simple model dependent on primordial development

In an analysis of leaf development of leek plants grown in the field in 1988, successive leaves initiated, appeared (tip and ligule) and senesced at equal intervals of accumulated temperature/thermal time. These intervals corresponded to a plastochron of 92°C days and phyllochrons of 135 (tip) and 233 (ligule) °C days. The rate of appearance of ligules was exactly equal to the rate of leaf senescence, with the result that the number of fully-expanded leaves per plant remained constant at 1.4. These data, which were compatible with results from previous seasons, were used to develop a model of the interrelationships between primordium initiation at the shoot apex and subsequent events in the development of individual leaves. Primordium initiation is considered to be the primary controlling event in the life of a leaf, and the processes of tip appearance, ligule appearance and death can be predicted from knowledge of the number of primordia which have been initiated, without reference to the environment. A model of canopy expansion, based on the central role of the shoot apex, was developed using the temperature relations of primordium initiation and additional data on leaf expansion and leaf dimensions. Leaf area indices computed in this way provided a satisfactory simulation of the thermal-time course of leaf area index observed in a previous season, 1985.     

Seed mass and light-demand: the need to control for soil–type and plant stature

Studies on whether or not species which need more light for establishment have smaller seeds should be made between plants of similar mature height living in the same soil and macroclimate. Salisbury's classic comparisons confused differences in light-requirement during establishment with differences in mature height and in the supply of soil resources.     

Effects of NO3– and BAP on organogenesis in tissue-cultured shoot primordia induced from shoot apices of Utricularia praelonga St. Hil.

The effects of NO₃ ^– and BAP on organogenesis in shoot primordia of Utricularia praelonga subcultured in B5 liquid medium were studied. In B5 liquid basal medium supplemented with 24.73 mM KNO₃ and 2.0 mg/l BAP the subcultured shoot primordia continuously multiplied into numerous small, globular masses, while with dilution of the KNO₃ to 3 mM organogenesis was promoted. Pulse treatment of the shoot primordia with 3 mM KNO₃ in B5 liquid medium for 72 h and then transplantation to the B5 basal liquid-medium induced meristemoids in this tissue. When the shoot primordia regenerated meristemoids, they never reverted back into the proliferation cycle. The addition of BAP in the B5 liquid medium with 3 mM KNO₃ regulated the differentiation rate of the stems and leaves in the meristemoids induced in the masses of shoot primordia. The control produced 3 parts stems to 1 part leaves; medium with 0.02 mg/l BAP regenerated approximately 2 parts stems and 1 part leaves; that of 0.20 mg/l BAP 1 part stems and 2 parts leaves; and medium with 2.00 mg/l BAP regenerated leaves only. Received: 17 September 1997 / Revision received: 30 October 1997 / Accepted: 18 November 1997