Cytokinin Profiles in the Conifer Tree <Emphasis Type="Italic">Abies nordmanniana</Emphasis>: Whole-Plant Relations in Year-Round Perspective

Conifer trees are routinely manipulated hormonally to increase flowering, branching, or adjust crown shape for production purposes. This survey of internal cytokinin levels provides a background for such treatments in Abies nordmanniana, a tree of great economic interest. Reference points in the crown and root system were sampled destructively in 4- and 6-year-old trees and analyzed for a range of cytokinins by LC-MS/MS. No seasonal patterns were detected in the root samples, and a major portion of cytokinin was in conjugated forms. Dramatic and consistent seasonal changes occurred in the crown, at levels 17–65 times higher than in the root. Predominant among crown cytokinins was ZR, except in the needles where IPR was also prominent. Within the crown, cytokinin profiles in different organs differed consistently. The leader bud showed a pronounced mid-June minimum, and a maximum later in summer. Subapical buds showed the same June minimum but peaked in mid autumn at a much lower level. Maxima in these buds were preceded by peaks in the subapical stem. Parallel patterns were observed in homologous tissues on branches.This pattern is consistent with two surges beginning in the uppermost stem tissues leading to subsequent accumulation or stimulated production within the buds. Strong differential hormonal profiles between adjacent buds with different fates agree with recent evidence of localized cytokinin production. The data suggest a reduced role of root-derived cytokinins in crown development. Practical cytokinin treatments for crown-shape regulation require close attention to dosage as well as precise timing and positioning.     

Uptake and Presentation of Myelin Basic Protein by Normal Human B Cells

B cells may play both pathogenic and protective roles in T-cell mediated autoimmune diseases such as multiple sclerosis (MS). These functions relate to the ability of B cells to bind and present antigens. Under serum-free conditions we observed that 3–4% of circulating B cells from healthy donors were capable of binding the MS-associated self-antigen myelin basic protein (MBP) and of presenting the immunodominant peptide MBP85-99, as determined by staining with the mAb MK16 recognising the peptide presented by HLA-DR15-positive cells. In the presence of serum, however, the majority of B cells bound MBP in a complement-dependent manner, and almost half of the B cells became engaged in presentation of MBP85-99. Even though complement receptor 1 (CR1, CD35) and CR2 (CD21) both contributed to binding of MBP to B cells, only CR2 was important for the subsequent presentation of MBP85-99. A high proportion of MBP85-99 presenting B cells expressed CD27, and showed increased expression of CD86 compared to non-presenting B cells. MBP-pulsed B cells induced a low frequency of IL-10-producing CD4+ T cells in 3 out of 6 donors, indicating an immunoregulatory role of B cells presenting MBP-derived peptides. The mechanisms described here refute the general assumption that B-cell presentation of self-antigens requires uptake via specific B-cell receptors, and may be important for maintenance of tolerance as well as for driving T-cell responses in autoimmune diseases.     

Metabolism of Oat Leaves during Senescence : VIII. The Role of L-Serine in Modifying Senescence

The mechanism whereby l-serine specifically promotes the dark senescence of detached oat (Avena) leaves has been examined. The fact that this promotion is strong in darkness but very weak in white light has been explained, at least in part, by the finding that added serine is partly converted to reducing sugars in light. Labeled serine gives rise to ¹⁴C-sugars and ¹⁴CO₂. In the absence of CO₂, serine does cause chlorophyll loss in light and undergoes a decreased conversion to sugar.     

Can Community Members Identify Tropical Tree Species for REDD+ Carbon and Biodiversity Measurements?

Biodiversity conservation is a required co-benefit of REDD+. Biodiversity monitoring is therefore needed, yet in most areas it will be constrained by limitations in the available human professional and financial resources. REDD+ programs that use forest plots for biomass monitoring may be able to take advantage of the same data for detecting changes in the tree diversity, using the richness and abundance of canopy trees as a proxy for biodiversity. If local community members are already assessing the above-ground biomass in a representative network of forest vegetation plots, it may require minimal further effort to collect data on the diversity of trees. We compare community members and trained scientists’ data on tree diversity in permanent vegetation plots in montane forest in Yunnan, China. We show that local community members here can collect tree diversity data of comparable quality to trained botanists, at one third the cost. Without access to herbaria, identification guides or the Internet, community members could provide the ethno-taxonomical names for 95% of 1071 trees in 60 vegetation plots. Moreover, we show that the community-led survey spent 89% of the expenses at village level as opposed to 23% of funds in the monitoring by botanists. In participatory REDD+ programs in areas where community members demonstrate great knowledge of forest trees, community-based collection of tree diversity data can be a cost-effective approach for obtaining tree diversity information.     

Multiple actions of abscisic acid in senescence of oat leaves

The modifications induced by abscisic acid (ABA) on the senescence of oat leaves in darkness have been studied and are compared with its well-known effects in light. Contrary to the action in light, ABA preserves chlorophyll (Chl) in the dark almost as well as kinetin. Chlorophylla is decolorized more extensively thanb, and the content ofb is maintained by ABA almost at its initial level for 4 days. ABA also prevents proteolysis in darkness just as completely as chlorophyll loss, the relationship of both breakdown processes to ABA concentration being strictly log-linear over the range from 1 to 100 M. In line with this action, ABA inhibits formation of the neutral protease in the dark but not in the light. The data suggest that ABA and kinetin operate to preserve chlorophyll and protein by different mechanisms, since their actions are neither independent nor synergistic but actually interfere with one another. In this connection, protein values given by the Lowry and Bradford methods have been compared. In parallel with the effect on senescence, ABA slowly opens the stomata in the dark. This effect increases with time, and by day 3 the stomata in ABA are as open as in leaves on water in light. Thus all these effects of ABA in darkness are strikingly opposite to those commonly observed on leaves in natural lighting. In addition, ABA powerfully inhibits the formation of ethylene in the dark by the detached oat leaves, and this inhibition also tends to increase with time. Finally, a slight antagonism to ABA's action on senescence is exerted byp-coumaric acid in the light but not in the dark.     

Pea seedling growth and development regulated by cotyledons and modified by irradiance

Growth and development of hydroponically grown pea seedlings ( Pisum sativum L. cv. Alaska) were measured using stem and root length as well as number of leaves and lateral roots. The growth was dependent on the presence of cotyledons and was modulated by the irradiance. All plants were grown in a full nutrient solution. If grown at low irradiance (73 μmol m^-2s^-1) they depended more and for a longer time on the cotyledons than plants grown at high irradiance (220 μmol m^-2s^-1). Low irradiance caused stem elongation but decreased root length and number of lateral roots as compared to plants grown at high irradiance. The dark respiration of the leaves was measured as oxygen uptake. In plants grown at the low irradiance, excision of the cotyledons caused the rate of oxygen uptake to increase by a factor of three, and the increase was sensitive to cyanide. Decotyledonized plants showed a high respiration rate and a diminished leaf growth for their entire life cycle. CO₂ fixation also increased in decotyledonized pea seedlings grown at either irradiance. The mobilization of food reserves from the seeds was positively correlated to seed dry weight, but only if the plants were grown at 73 μmol m^-2s^-1. Increasing dry weight of the seed enhanced top growth, whereas root growth was depressed, so that top and root responds differently with regard to that part of growth which depends on mobilization of reserves from the seed.     

“Lateral Control”: Phytohormone Relations in the Conifer Treetop and the Short- and Long-Term Effects of Bud Excision in Abies nordmanniana

In a conifer tree, such as Nordmann fir, Abies nordmanniana Spach, the leader bud and its immediate surroundings play a decisive role in crown architecture. As subapical branch buds are segregated from the leader meristem, resource allocation between ortho- and plagiotropic growth is determined. The relationship between treetop buds in young trees was studied in the natural state and after surgical removal in early July of either the leader bud (decapitation) or the subapical whorl branch buds (destipitation). The two bud types showed consistent cytokinin profile differences but similar seasonal dynamics in cytokinins and auxin (IAA). After bud excision, ZRP increased dramatically in the subapical stem within 1 h, followed by ZR within 1 week. Supernormal levels of ZR were maintained through autumn and persisted in spring in the destipitated trees, but had returned to normal in the decapitated trees. The treetop buds remaining after bud excision experienced an immediate decrease in most cytokinins, followed, however, by a large surplus later in the season. The following spring this high level persisted in the leader bud of destipitated trees, but not in whorl buds of decapitated trees. Conspicuous growth pattern changes followed from destipitation, but few from decapitation. Growth reactions suggest that resource allocation to main branch buds inhibits leader growth in normal trees, a kind of “lateral control.” Auxin and ABA content in buds and stems was largely unaffected by treatments. Data suggest that subapical leader tissues beneath the apical bud group are a primary source of cytokinin regulation.