Fritz Bangerth

Hormonal status of maize initial explants and of the embryogenic and non-embryogenic callus cultures derived from them as related to morphogenesis in vitro

Endogenous hormone levels (indole-3-acetic acid [IAA], abscisic acid [ABA], gibberellins (1, 3) and (20) [GAs], zeatin/zeatin riboside [Z/ZR] and N(6)[Delta(2)-isopentenyl] adenine/N(6)[Delta(2)-isopentenyl] adenosine; [iP/iPA]) were analysed in immature maize zygotic embryos of two maize (Zea mays L.) genotypes, known for their distinct ability to generate embryogenic (E) callus. No differences were found among genotypes in the hormone contents of the embryos. These embryos were also used as initial explants to establish callus cultures. E and non-embryogenic (NE) calli were obtained from the competent genotype (A188), while only NE callus was produced by the incompetent one (B73). The morphogenetic competence of each callus type was evaluated by transferring some segments to regeneration conditions. When analysing the endogenous hormone levels in the various callus types generated in each genotype, it was found that only differences in the IAA levels accounted for variations in the morphogenic properties of the calli. Higher levels of endogenous IAA were typical of embryogenic callus cultures. It was also observed, that a loss in the embryogenic competence of the calli, due to a prolonged time of culture, occurred concomitantly with a reduction in the IAA levels, practically to the levels found in the non-embryogenic calli.

A Role for Auxin and Auxin Transport Inhibitors on the Ca Content of Artificially Induced Parthenocarpic Fruits

Artificially induced parthenocarpic fruits of apples, pears and tomatoes, as well as seeded fruits treated with 2,3,5-triiodobenzoic acid, frequently show symptoms of Ca deficiency and a low Ca content. It was concluded that auxins, probably produced by the seeds, play a significant role in Ca translocation into fruits. Exogenous indoleacetic acid but not 4-chlorophenoxyacetic acid applications could replace the effect of seeds in this respect. Auxin transport, rather than auxin accumulation, seems to be necessary for Ca transport, as can be concluded from the effect of auxin transport inhibitors.

Genetic relationships of avocado (Persea americana Mill.) using RAPD markers

RAPD (randomly amplified polymorphic DNA) analysis was carried out on 16 accessions representing the three ecological races of avocado (Persea americana Mill.), and one accession of P. schiedeana Nees. Twenty two preselected primers produced 133 polymorphic DNA fragments in the RAPD assay of the avocado accessions. One primer was identified which could differentiate each of the avocado accessions. Potentially race-specific markers for each of the Mexican, Guatemalan, and West Indian races, have been detected. A Jaccards similarity coefficient matrix was generated and a dendrogram constructed using UPGMA (unweighted pair-group method of arithmetic averages) cluster analysis. Percentage similarity between avocado accessions ranged from 46% to 85%. The lowest similarity (between 22% and 29%) was revealed between P. schiedeana and any P. americana accession. Average similarity within races of avocado was 75% for the Mexican race, 71% for the West Indian race and 73% for the Guatemalan race. Average similarity between races ranged from 53% to 58%. The dendrogram identified three groups, representing the races of avocado. These results are in concordance with the present classification of avocado into three subspecies (varieties) of P. americana, namely drymifolia, americana, and guatemalensis, corresponding to the Mexican, West Indian and Guatemalan races, respectively, and confirm the separate species status of P. schiedeana. We conclude that RAPD markers may be useful for the classification of avocado and for the assessment of genetic diversity of avocado germplasm.

The effect of different partial pressures of oxygen and ethylene on the ripening of tomato fruits

Abstract Tomato fruits were stored in a low (hypobaric) pressure system (LPS), ventilated with different oxygen and ethylene concentrations. The effect of these factors on different ripening-parameters (respiration, chlorophyll degradation, lycopene synthesis, fruit firmness and pectic enzyme activities) was investigated. Ethylene had a definite effect on most but not all of these parameters, even at the low oxygen pressure used in this system. The reduction in oxygen as well as in ethylene partial pressures was responsible for the observed retardation of tomato fruit ripening at hypobaric conditions.

Effect of hydrogen cyanamide on the endogenous hormonal content of pea seedlings (Pisum sativum L.)

Hydrogen cyanamide (HC) has been used to break bud and seed dormancy and to improve rooting in several species, responses usually associated with the action of plant hormones. However, very few studies have measured endogenous hormones after HC treatment. Therefore, pea (Pisum sativum L.) seedlings with two fully developed internodes above the first leaf were sprayed with 0, 0.1 and 0.3% (v/v) HC. Endogenous concentration of indole-3-acetic acid (IAA), abscisic acid (ABA), zeatin/zeatin riboside and N 6 (∆ 2 -isopentenyl) adenine/ N 6 (∆ 2 -isopentenyl) adenosine were measured by radioimmunoassay 31 and 80 h after HC treatment. A significant increase in ABA and cytokinin (CK) levels was observed 31 h after treating the plants with 0.3% HC. Small necrotic spots were also noticed in this treatment, thus revealing a toxic effect of this treatment. Additionally, at 80 h, a significant increase in IAA was found for both HC concentrations applied. The action of HC upon ABA, CKs and IAA endogenous levels is discussed.

UV-induced peroxidase and phenylalanine ammonia-lyase activity and phaseollin accumulation in leaves of Phaseolus vulgaris L. in relation to ethylene

Abstract Attached or detached leaves of bean (Phaseolus vulgaris L.) were irradiated with short-wave UV light (254 nm) which resulted in increased ethylene production, increased activity of soluble and ionically bound peroxidase, increased activity of phenylalanine ammonia-lyase and an accumulation of phaseollin, accompanied by bronzing of these leaves. In order to evaluate the role of ethylene in this process, plants were pretreated with 0.5 mM aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, or with 0.45 mM 5-methyl-7-chloro-4-ethoxycarboxymethoxy-2,1,3-benzothiodiazole (DU), a presumed inhibitor of ethylene action. Both compounds showed an inhibitory effect on UV-induced ethylene production. DU stimulated UV-induced peroxidase activity, whereas AVG seemed to decrease UV-induced peroxidase activity. DU and AVG had only a weak inhibitory effect on UV-induced PAL activity. Both compounds retarded slightly the accumulation of phaseollin and the appearance of necrotic symptoms in UV-irradiated bean leaves. Ethephon treatment (500 or 1000 ppm) failed to induce the accumulation of phaseollin in attached or detached leaves of bean. The role of ethylene in UV-induced peroxidase and phenylalanine ammonia-lyase (PAL) activity and accumulation of phaseollin in bean leaves is discussed.

The Plant-Physiological Basis of Flower Induction in the Control of Fruit Production

In the last four years, research has focused on off-season flower induction of longan, lychee and mango trees (Chapter 3.3). In order to achieve control over the flower induction process of fruit trees, it is necessary to address the key factors responsible for the transition from vegetative to generative bud development. Various, partly competing theories have been developed in the past about the physiological ‘Who’s Who’ in flower induction (Bernier et al., 1993). One theory favours the role of carbohydrates, which need to be present in sufficient amounts as a prerequisite for flower induction (Sachs, 1977). Other theories of flower induction focus either on the genetic control of a developmental switch from vegetative to generative development (Levy and Dean, 1998), control by particular hormones (Bernier et al., 2002), the existence of specific promoting or inhibiting factors or a mixture of both. However these theories do not apply to adult perennial fruit trees (Goldschmidt and Samach, 2004). Knowledge and understanding of the hormonal changes associated with the treatments previously described (Chapter 3.3) can be beneficial for future trials to induce flowering in mango, lychee and other fruit trees.

Strategies for Flower Induction to Improve Orchard Productivity: From Compensation of Alternate Bearing to Off-Season Fruit Production

Due to alternate and irregular bearing of fruit trees, which occurs at various extent amongst different species and cultivars, the yield of many species of fruit tree is erratic. Uncertainties regarding the time of harvest and the quality and quantity of fruit can seriously affect the marketability of the product (Monselise and Goldschmidt, 1982; Westwood, 1995; Subhadrabandhu, 1999; Souza et al., 2004). Unfavourable climatic conditions during flower induction (FI) or the flowering period are amongst the most important causes of this phenomenon. Often large areas or even whole countries face the same problem simultaneously leading to overproduction and low prices in one year and a low return from fruit production the next. Equalising these fluctuations therefore would help to make fruit production more profitable and sustainable. Another option for raising the return from fruit production would be to extend or totally shift the harvest season by artificially influencing conventional and off-season flowering.

Stabilisation of Fruit Production by Optimised Plant Nutrition

In the orchards of small-scale farmers in northern Thailand, low input of fertiliser often results in insufficient, low quality fruit yields particularly from older trees. This generally low input of fertilisers and other agrochemicals has been well documented. Deficiencies of micronutrients such as boron (B) and zinc (Zn) have also been frequently reported for Southeast Asia (Dong et al., 1997; Bahadur et al., 1998) and might affect flower induction, fruit set and fruit growth.