Browsing by Subject "Knospe"

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Mechanisms of frost adaptation and freeze damage in grapevine buds
(2002) Badulescu Valle, Radu Virgil; Blaich, Rolf
Mechanisms of frost hardening in compound (latent) buds of the grapevine cultivar ?Bacchus? were tested with different methods during three winters. The investigated parameters were LTE/HTE (low temperature exotherm/high temperature exotherm), water content, starch, sugar- and anions combination and bud histology. Water content from wood and buds was determined regularly every 2 weeks from March 1998 until Mai 2000. The lowest water content in wood and buds (about 40 %) was found between November and February. In general shoot sections and buds from the apical shoot area contained less water than in the basal area. Sugars and anions were analyzed with HPLC. The highest concentrations of soluble sugars were found in basal buds of the shoot, the lowest concentration in buds of the apical shoot area. Sucrose was the predominant soluble sugar, it was accompanied by glucose, fructose, sucrose, raffinose, and also stacchyose which was hitherto not described for grapevine buds. The concentration of soluble sugars increased during autumn and reached its maximum (around 150 mg/g dry matter) in November/December until the beginning of January then it decreased again to around 30 mg/g at bud burst. The predominant anion was sulphate while chloride could be detected only in traces. The anions reached their maximum at the beginning of January and in mid April. To evaluate the exotherm measuring method, model experiments were carried out with water drops (1µl) on filter paper and with small plant parts (leaf, stems, flower parts). Both the plant parts and the destilled water on the cellulose fiber freeze mainly between ?8 and ?15°C (an influence of the low osmotic value of the plant sap could not be found). After the first freezing the specimen were thawed and freezing repeated. The freezing points of the first and the second freezing cycle were significantly correlated. This shows that freezing does not occur at random, but is determined by ice nucleation sites characteristic for each sample. These sites even survive the physical destruction of the cells by the ice cristals. Further model experiments were carried out to get indications on possible barriers to ice cristal growth in plant tissue. Exotherm analysis was used to determine the freezing point of grapevine buds which is accompanied by a transient temperature rise called exotherm. The grapevine buds show 2 or more exotherms, one or two HTEs (high temperature exotherms) between ? 5 °C and ?10°C and the LTE (low temperature exotherm, sometimes more than one ) between ?10°C and ?25°C depending on the frost adaption of the buds. The HTEs are assumed to indicate the freezing of surface water or apoplastic water in the subtending tissue (bud pad), whereas the LTE (or LTEs) seem to be caused by freezing of the primary (and secondary) buds (shoot primordiy of the compound bud). The temperature minimum of the LTEs (down to ? 25 °C) is reached in January/February and is not influenced by humidity which, however, changes the THE values occuring usually around ? 10 ° and ? 4 °C, which are influenced by water in the bud scales. The LTEs of the buds in the lower area of the shoot were higher as compared to the buds in the middle and upper area of the shoot. The LTE analysis clearly shows the frost adaptation of the latent buds which usually reaches a maximum by the end of January but a clear relation to the changing air temperatures could not be established. Histological and cytological analyses were used to test for frost damage in bud parts and for changes during the cold adaptation. A modified staining method was developed to differentiate the cells. During automn and winter the buds contained a lot of starch grains which dissolved at bud burst. A permeability barrier between bud pad and shoot primordia could not be found, however it could be directly shown, that a HTE causes no cell damage in the buds, while after the appearence of the LTE(s) a disintegration of protoplasts in primary and secondary buds could be found. This is a direct evidence that LTEs indicates the death of the eyes in the complex grapevine bud. If after the appearance of the HTE the buds were held one day at this temperature before further cooling, no LTEs would appear. This and similar observations during the frost storage of grapevine cuttings is discussed in terms of the (harmless) ice formation in the bud base at moderate minus temperatures which would result in a freeze drying effect due to the lower water potential of the bud pad (in comparison to the non frozen eyes) and a further increase of the frost resistance of the growing points. If frost adapted grapevine shoots from the field were kept at 20°C deacclimation occurred after about 10 days. Accidentally wetted buds showed exotherms above ?4°C. In these buds and the watering water ice nucleating bacteria (Pseudomonas fluorescens) could be found.
Physiological, metabolic and molecular basis of biennial bearing in apple
(2023) Kofler, Julian; Zörb, Christian
Alternate or biennial bearing in apple (Malus ×domestica Borkh.) is characterized by ‘On’ years with high crop load and inhibited floral bud initiation and ‘Off’ years with little crop load and promoted formation of floral buds, respectively. Apple cultivars differ in their degree of biennial bearing behavior. The cropping irregularity has severe effects on quality and yield of apple harvests in commercial orchards and thereby directly poses an economic risk to apple growers. The aim of this study was to contribute to the understanding of the underlying mechanisms of biennial bearing in apple by analyzing the physiological processes in bud meristems during the time of flower bud induction. A field experiment was conducted during the growing seasons 2015 and 2016 and provided bud meristems of various developmental stages for a variety of analyses. The regular bearing cultivar ‘Royal Gala’ and the biennial bearing cultivar ‘Fuji’ allowed the comparison of two different developmental responses to high and low crop load treatments. Buds from 2-year-old spurs were sampled starting approximately four weeks after full bloom. Histological analysis of bud meristems successfully identified the time point of flower bud initiation in both cultivars at the experimental site. The onset of flower bud initiation was affected by crop load, cultivar and heat accumulation. While heavy cropping delayed the onset in ‘Royal Gala’ trees for 20 days compared to ‘Royal Gala’ trees with no crop load, bud initiation in heavy cropping ‘Fuji’ trees was negligible. ‘Fuji’ trees with no crop load started initiating buds 19 days earlier than ‘Royal Gala’ trees with the same cropping status. Proteomic profiling of the buds sampled during flower bud induction and during flower bud initiation revealed distinct differences in specific protein abundances depending on the cropping status. Buds from trees with a high crop load, where the flower bud initiation was inhibited and the buds primarily remained in a vegetative state, showed a decreased abundance of enzymes belonging to the phenylpropanoid and flavonoid pathways. Specifically, PAL was reduced, which could lead to less active auxin due to the reduced production of chlorogenic acid and thereby inhibiting flower bud formation. Furthermore, increased abundances of histone deacetylase and ferritins were also found in buds from high cropping trees, indicating that histone modification and building up enough iron storage capacities are involved in the vegetative bud development. Buds growing on non-cropping trees with a high rate of flower bud initiation, showed significantly higher concentrations of proteins involved in histone and DNA methylation. Metabolomic profiling and next-generation RNA sequencing showed that thiamine, chlorogenic acid, and an adenine derivative play a role in metabolic pathways promoting early flower bud development in apple, and that tryptophan was more abundant in buds collected from high-cropping trees compared to non-cropping trees. The selection of proteins, metabolites, and genes that the current work produced through its broad, non-targeted approach provides a comprehensive data base for future, more targeted analyses. The results of this study lay a thorough baseline to contribute to the identification of biological markers that are linked to a certain bearing behavior. Such markers can accelerate and facilitate breeding programs aimed at selecting apple cultivars, that are less prone to biennial bearing.