Anatomical and Biochemical Events duringin vitroRooting of Microcuttings from Juvenile and Mature Phases of Chestnut

A comparative study of thein vitrorooting process of chestnut(Castanea sativa)shoots of the same genotype exhibiting juvenile(easy-to-root) and mature (difficult-to-root) characteristicsis described. The two culture lines originated from shoots collectedfrom the base (juvenile) and crown (mature) of an 80-year-oldtree. Anatomically, juvenile and mature shoots had a similarstem structure at the time of excision, the main differencebeing that secondary phloem and xylem were more developed inmature than in juvenile shoots. A substantial reactivation ofcell division was observed in both shoot lines 48 h after theroot inductive treatment with indole-3-butyric acid. Meristemoidsand root primordia developed only in juvenile shoots, beginning3 d after the inductive treatment, and the first adventitiousroots emerged 10 d after treatment. However, in mature shootspericlinal divisions of cambial cells occurred, especially onthe phloem side, maintaining the normal orientation of the cambialderivatives. No meristemoids formed in this proliferating tissue.During the time course of the rooting process, more endogenousindole-3-acetic acid (IAA) was detected in mature than in juvenileshoots, indicating that the level of IAA is not the limitingfactor accounting for the lack of rooting capacity in matureshoots. The levels of polyamines (putrescine, spermine and spermidine)were also higher in mature than in juvenile shoots.Copyright1999 Annals of Botany Company Adventitious rooting, anatomy, auxins,Castanea sativaMill., chestnut, juvenile phase, mature phase, polyamines, tissue culture.     

Association between competition and facilitation processes and vegetation spatial patterns in alpha steppes

In semiarid ecosystems, the self-organized spatial patterns of plants associated with catastrophic shifts can emerge from a variety of processes. In this study, on moderate slopes where Stipa tenacissima cover was high, the self-organization of some of the typical species of semiarid Mediterranean matorral ( Phlomis purpurea , Sideritis oxteosylla, Helianthemum almeriense , and Brachypodium retusum ) was negatively correlated with Stipa cover. The extent of Stipa cover did not affect desert pioneer species, such as Artemisia herba-alba , Fagonia cretica , and Launaea lanifera . On pronounced slopes, the self-organizing structure of brushwood vegetation did not vary predictably with the amount of Stipa cover. We examined the competition/facilitation processes associated with self-organizing patterns in the dwarf shrub ( Phl. purpurea ) and the half shrub ( H. almeriense ). The developmental stability of H. almeriense was positively correlated with Stipa cover, which was expected because they are associated species in this seral thyme brushwood community. Indeed, facilitation processes were manifested by the developmental stability increases under the Stipa canopy, particularly on high slope areas, where Stipa is less competitive. In Phl. purpurea , negative feedback processes from competition with Stipa were manifested where Stipa cover was high and on low slopes (developmental instability increased). In general, competition with Stipa on low slopes tended to decrease plant self-organization.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 103–113.