Hormonal Profile in Vegetative and Floral Buds of Azalea: Levels of Polyamines, Gibberellins, and Cytokinins

The floral transition includes a complex system of factors that interact and involve various biochemical signals, including plant growth regulators. The physiological signals involved in the control of the floral transition have been sparsely studied and mainly in plant species whose genetics are poorly known. In this work, the role of polyamines, gibberellins, and cytokinins was investigated by analyzing their endogenous content in vegetative and floral buds of azalea. The results showed that there is a clear distinction between floral and vegetative buds with respect to the levels of these plant hormones, with floral buds containing higher amounts of conjugated polyamines, gibberellins (GAs) from the non-13-hydroxylation pathway (GA₉, GA₇, and GA₄), and cytokinins (particularly isopentenyl-type species), and vegetative buds containing higher amounts of free polyamines and gibberellins from the early 13-hydroxylation pathway and fewer cytokinins. In conclusion, there is a specific pattern of endogenous hormone profiles in both vegetative and floral bud development in azalea, which may be relevant for future research on the control of flowering by exogenous hormone applications.     

Seasonal, diurnal and rehydration-induced variation of pressure-volume relationships in Pseudotsuga menziesii

Seasonal and diurnal variation and rehydration effects of pressure-volume parameters in Pseudotsuga menziesii (Mirb.) Franco from a plantation in central Pennsylvania, USA, were evaluated during May-September, 1989. Predawn elastic modulus was lowest in overwintering and newly expanded shoots in May and June, respectively, whereas predawn osmotic potentials at full and zero turgor were lowest in May and in early September, following an August drought. Seasonal variation in predawn relative water content at zero turgor was highly correlated with increases and decreases in elastic modulus and osmotic potential. Diurnal osmotic adjustment resulted in nearly constant turgor pressure, despite decreases in bulk shoot water potential. Elastic modulus decreased diurnally on 1 August and increased on 3 September. Decreases in osmotic potential and/or elastic modulus on 24 June and 1 August lowered the relative water content at zero turgor. Plateaus in pressure-volume data caused by excess apoplastic water, were present in 67% of naturally rehydrated shoots and in all of the shoots artificially rehydrated for 3, 6, 12 and 24 h, and they increased in volume with rehydration time. Plateaus represented 80–95% of the excess apoplastic water lost during pressure-volume analysis. Correcting for plateaus via linear regression had no significant effect on osmotic potential at full turgor; however, uncorrected elastic modulus and relative water content at zero turgor were often significantly lower than the plateau-corrected values, particularly in artificially rehydrated shoots. Plateau-corrected osmotic potential at full turgor and osmotic potential at zero turgor were significantly higher in most artificially rehydrated shoots than in those naturally rehydrated as the result of loss of symplastic solutes. Corrected elastic modulus decreased following 12 and 24 h of rehydration and corrected relative water content at zero turgor increased in as little as 3 h of rehydration. These results indicate that seasonal and diurnal patterns of tissue-water parameters in Pseudotsuga menziesii vary with plant phenology and drought conditions, and that the length of rehydration period is an important consideration for pressure-volume studies.     

Crown closure affects endophytic leaf mycobiome compositional dynamics over time in Pseudotsuga menziesii var. menziesii

Old-growth Pseudotsuga menziesii var. menziesii forests produce complex environmental and spatial gradients along which biota assemble. Given this, it has been proposed that changes in the crown microenvironment are associated with different community assembly outcomes for needle fungi. Using high-throughput sequencing, the endophytic mycobiomes of needles were characterized for increasing ages of needles sampled along the boles of eight coastal Douglas-fir trees. Leveraging airborne light detection and ranging (LiDAR) data to create three-dimensional “point cloud” representations of tree crowns revealed that crown closure accounted for more fungal compositional variation than height in crown, and fungal richness and diversity were positively correlated with increasing crown closure. Supplementing the point clouds of each climbed tree with clouds from >5,000 randomly selected trees in the study area showed that fungal communities from closed portions of the crown were increasingly structured with needle age. These findings highlight the importance of the crown microenvironment in the development of foliar fungal communities for a foundation tree species.     

Species-mediated soil moisture availability and patchy establishment of Pseudotsuga menziesii in chaparral

The occurrence of mature individuals of Pseudotsuga menziesii in stands of Arctostaphylos species mark the initial stages of mixed evergreen forest invasion into chaparral in central coastal California. We planted two cohorts of P. menziesii seeds at three sites under stands of two Arctostaphylos species and Adenostoma fasciculatum in order to determine whether first-year seedling emergence and survival, particularly during the regular summer drought, underlie the spatial distribution of mature trees observed in chaparral. Regardless of the chaparral species they were planted under, P. menziesii seeds that were not protected from vertebrate predation displayed very little emergence and no survival. In contrast, emergence of P. menziesii that were protected from vertebrate predators was much higher but still did not significantly differ among the three chaparral species. However, survival of protected seedlings under Arctostaphylos glandulosa was much greater than under A. fasciculatum, with intermediate survival under Arctostaphylos montana. While mortality of protected seedlings due to insect herbivory, fungal infection, and disturbance displayed no consistent patterns, summer drought mortality appeared to drive the patterns of survival of P. menziesii under the different chaparral species. These emergence, mortality, and survival data suggest that spatial patterns of P. menziesii recruitment in chaparral are driven by first-year summer drought seedling mortality, but only in years when seeds and seedlings are released from vertebrate predation pressure. Because the first-year drought mortality and survival patterns of P. menziesii seedlings differed strongly depending on the chaparral species, we examined the additional hypothesis that these patterns are associated with differences in the availability of soil moisture under different chaparral species. Both higher survival and lower drought mortality of P. menziesii seedlings were associated with higher soil water potential under Arctostaphylos stands during the summer drought, especially in the subsurface soil. The data suggest that Arctostaphylos stands, particularly stands of A. glandulosa, ameliorate xeric summer conditions to a degree that facilitates first-year establishment of P. menziesii and strongly influences spatial distribution of mature trees. Received: 18 September 1998 / Accepted: 23 December 1998     

Genetic differentiation in carbon isotope discrimination and gas exchange in Pseudotsuga menziesii

Patterns of genetic variation in gas-exchange physiology were analyzed in a 15-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation that contains 25 populations grown from seed collected from across the natural distribution of the species. Seed was collected from 33°30 to 53°12 north latitude and from 170 m to 2930 m above sea level, and from the coastal and interior (Rocky Mountain) varieties of the species. Carbon isotope discrimination () ranged from 19.70() to 22.43() and was closely related to geographic location of the seed source. The coastal variety (20.50 (SE=0.21)) was not significantly different from the interior variety (20.91 (0.15)). Instead, most variation was found within the interior variety; populations from the southern Rockies had the highest discrimination (21.53 (0.20)) (lowest water-use efficiency). Carbon isotope discrimination (), stomatal conductance to water vapor (g), the ratio of intercellular to ambient CO₂ concentration (c_i/c_a), and intrinsic water-use efficiency (A/g) were all correlated with altitude of origin (r=0.76, 0.73, 0.74, and –0.63 respectively); all were statistically significant at the 0.01 level. The same variables were correlated with both height and diameter at age 15 (all at P0.0005). Observed patterns in the common garden did not conform to our expectation of higher WUE, measured by both A/g and , in trees from the drier habitats of the interior, nor did they agree with published in situ observations of decreasing g and with altitude. The genetic effect opposes the altitudinal one, leading to some degree of homeostasis in physiological characteri tics in situ.     

Effects of ovular secretions on pollen in Pseudotsuga menziesii (Pinaceae)

Effects of ovular secretions on pollen grains were examined in Pseudotsuga menziesii. The exine is cast off in the micropylar canal. A membranelike structure covers parts of pollen grains and appears to protect them. The outer intine consists of fibrous materials, but it also shows a thicker filamentous appearance in some ovules during pollen elongation. The inner intine is electron-dense. Its fibrous nature is occasionally visible. Dissolution of the outer intine varies in amount and manner in ovules from different trees. The plasma membrane near the pollen wall alternatively appears normal and distorted. These different morphologies of the outer intine and of the plasma membrane are considered to result from secretions from the ovule. The outer intine may contain electron-dense globules that are formed in the tube cell and traverse the inner intine. Pollen tube formation appears to be triggered by a secretion from the ovule. Cross-pollinated grains are less distorted compared with self-pollinated grains.     

Nuclear bodies in Douglas fir (Pseudotsuga menziesii Mirb.) microspores

The identification of nucleolar proteins and immunocytochemical localization of small nuclear ribonucleoprotein (snRNP) elements revealed the presence of three types of nuclear bodies in Douglas fir microspore nuclei. One type consists of structures resembling Cajal bodies (CBs) and contains nucleolar proteins as well as snRNPs and U2 snRNA. The second type is bizonal bodies, which are nuclear bodies also linked with the splicing system. The bizonal body comprises two parts: the first contains Sm proteins and stains strongly with silver stain, and the second resembles CBs in terms of the degree of silver staining and molecular composition. Douglas fir is the second species after larch where the presence of bizonal bodies has been demonstrated. Pseudotsuga menziesii Mirb and Larix decidua Mill are species with one of the longest microsporogenesis processes known in plants. The presence of bizonal bodies in both species may be linked to the intensification of the splicing processes in microspores with an exceptionally long cell cycle. The third type of structure is dense bodies, whose morphology and degree of silver staining strongly indicate their functional and spatial relationship to the dense part of bizonal bodies.     

Detection and identification of gibberellins in Douglas fir (Pseudotsuga menziesii) shoots

Extracts of Douglas fir ( Pseudotsuga menziesii [Mirb.] Franco) shoots were purified by reversed and normal phase HPLC; gibberellin (GA)-like compounds detected by radioimmunoassay with antibodies against GA₄ and the Tan-ginbozu dwarf rice micro-drop biossay were analyzed by GC-MS. Three major components were identified as GA₄, GA₇, and GA₉ while smaller amounts of GA¹, GA₃ and putative GA⁹-glucosyl ester were also present.     

Induced compression wood formation in Douglas fir (Pseudotsuga menziesii) in microgravity.

In the microgravity environment of the Space Shuttle Columbia (Life and Microgravity Mission STS-78), were grown 1-year-old Douglas fir and loblolly pine plants in a NASA plant growth facility. Several plants were harnessed (at 45 degrees ) to establish if compression wood biosynthesis, involving altered cellulose and lignin deposition and cell wall structure would occur under those conditions of induced mechanical stress. Selected plants were harnessed at day 2 in orbit, with stem sections of specific plants harvested and fixed for subsequent microscopic analyses on days 8, 10 and 15. At the end of the total space mission period (17 days), the remaining healthy harnessed plants and their vertical (upright) controls were harvested and fixed on earth. All harnessed (at 45 degrees ) plant specimens, whether grown at 1 g or in microgravity, formed compression wood. Moreover, not only the cambial cells but also the developing tracheid cells underwent significant morphological changes. This indicated that the developing tracheids from the primary cell wall expansion stage to the fully lignified maturation stage are involved in the perception and transduction of the stimuli stipulating the need for alteration of cell wall architecture. It is thus apparent that, even in a microgravity environment, woody plants can make appropriate corrections to compensate for stress gradients introduced by mechanical bending, thereby enabling compression wood to be formed. The evolutionary implications of these findings are discussed in terms of "variability" in cell wall biosynthesis.     

Investigations into the Possibility that Potato Buds Synthesize Cytokinins

In an attempt to determine whether potato buds synthesize cytokinins,tubers and potato pieces were subjected to conditions whichboth retard and accelerate bud development. Cytokinin activitywas recorded in the tubers and sprouts under different experimentalconditions. Most of the compounds detected had chromatographicproperties resembling those of zeatin, zeatin riboside, andzeatin glucoside. It would appear as if the buds and sproutsdo not synthesize cytokinins. Initial bud growth may be dependenton the supply of cytokinins within the mother tubers, whilethe increase in the sprouts could be the result of root developmentat their basal ends.     

Effect of Severity of Defoliation on the Viability of Reproductive and Vegetative Axillary Buds of Trifolium repens L.

This glasshouse experiment was performed to assess the effectsof a range of constant defoliation regimes applied to cuttingsof a single large-leaved genotype ofTrifolium repens L. on theviability of its axillary buds. Plants were established to comprisea single main stolon (axillary branches were removed) and defoliationtreatments were applied by removing the older (basal) leavesuntil leaf complements of 1·0, 1·5, 2·0,2·5, 3·0 or all leaves (control) remained. Basalleaves were subsequently removed as necessary to maintain thetarget leaf complements. Only severe defoliation (leaf complements of 1·0 and1·5) induced a loss of viability in axillary buds. Lossof viability was greatest in reproductive buds present withinthe apical bud when the treatments were first imposed. Althoughthe most severe treatment (leaf complement 1·0) resultedin death of half the plants, in plants surviving that treatment,death of vegetative axillary buds was restricted to 21% of thevegetative buds at the three youngest node positions withinthe apical bud at the time of treatment application. No othertreatment induced any loss of viability of vegetative buds.There was no loss of viability of axillary buds at nodes formedafter the treatments were imposed. The frequency of initiationof inflorescences at nodes formed after treatments were imposeddecreased as defoliation severity increased. Severe defoliation resulted in marked changes in plant morphologyindicative of a sharp decrease in availability of intraplantresources. It was concluded that under severe defoliation: (1)the potential for vegetative growth (as represented by viablevegetative axillary buds) was maintained at the expense of reproductivegrowth; and (2) that the loss of viability of axillary budswas associated with the sudden changes in physiological processesinduced by defoliation as there was no loss of viability inbuds formed after plants had adjusted their phenotype to oneof smaller size. Trifolium repens L.; white clover; defoliation; axillary buds; viability; inflorescences