Acram Taji

Anatomy and physiology of graft incompatibility in solanaceous plants

Summary Graft incompatibility in solanaceous plants was investigated using representative cultivars of tomato (Solanum lycopersicum L.), eggplant (Solanum melongena L.), and pepper (Capsicum annuum L.). Evaluations of the extent of graft (in)compatibility were made by examining survival percentages, fruit yields, and fruit quality in grafted plants. Tomato/pepper (scion/rootstock) and pepper/tomato grafts were considered severely incompatible, and the tomato/eggplant and eggplant/tomato grafts were considered moderately incompatible, when compared with the compatible homo-specific graft combinations of tomato/tomato, eggplant/eggplant, and pepper/pepper.Three, or 3 and 6 weeks after grafting, the dry weights of scions and rootstocks, carbohydrate concentrations in stems above and below the graft unions, scion mineral nutrient concentrations, water potentials of scions, and xylem hydraulic conductivities were measured in the grafted plants. The anatomy of the graft unions was also observed. Growth inhibition and high mortality in tomato/pepper and pepper/tomato grafts (i.e., severe graft incompatibility) was due to discontinuities in the vascular bundles at the graft union, which prevented the translocation of assimilates, mineral nutrients, and water between scions and rootstocks. Reductions in fruit yield and/or fruit quality of tomato/eggplant and eggplant/tomato grafts (i.e., moderate graft incompatibility) may have been due to differences in the requirements for assimilates and mineral nutrients between tomato and eggplant. Plant responses to graft incompatibility varied in solanaceous plants depending on the scion and rootstock combination.

Production of four commercially cultivated Echinacea species by different methods of in vitro regeneration

Summary Efficient in vitro procedures for mass propagation of four commercially important Echinacea species have been deveoped. Plants of E. angustifolia, E. pallida, E. paradoxa and E. purpurea were regenerated by three methods, namely axillary bud proliferation, adventitious shoot formation and somatic embyrogenesis. Shoot tips obtained from in vitro germinated seedlings, adventitious shoots or somatic embryo-derived plantlets, when cultured on Murashige and Skoog medium enriched with 1 μM 6-benzylaminopurine, 2 μM kinetin, 0.5 μM indole-3-butyric acid and 4 mg–1 paclobutrazol multiplied three-fold within 3–4 weeks in culture. Incorporation of paclobutrazol in the shoot multiplication medium was necessary to recover healthy and robust shoots suitable for rooting. Direct, high-frequency shoot formation on intact leaves of shoots grown on 6-benzylaminopurine and kinetin-supplemented media, an unusual and novel observation made in this study, occurred in all the species studied. Rooting of in vitro developed shoots was achieved relatively easily with Murashige and Skoog basal medium rather than with auxin-enriched media. Culturing of hypocotyl explants on medium containing 3,6-dichloro-o-anisic acid (commonly known as dicamba), or 2,4-dichlorophenoxyacetic acid, resulted in direct somatic embryogenesis in all the species examined. The presence of cytokinin was required for somatic embryo germination, but further development of germinated somatic embryos into normal plantlets occurred in Murashige and Skoog medium. We conclude that the procedures described here could be used for rapid propagation as well as genetic transformation of commerically cultivated Echinacea species.

Tripogon loliiformis elicits a rapid physiological and structural response to dehydration for desiccation tolerance

Resurrection plants can withstand extreme dehydration to an air-dry state and then recover upon receiving water. Tripogon loliiformis (F.Muell.) C.E.Hubb. is a largely uncharacterised native Australian desiccation-tolerant grass that resurrects from the desiccated state within 72h. Using a combination of structural and physiological techniques the structural and physiological features that enable T. loliiformis to tolerate desiccation were investigated. These features include: (i) a myriad of structural changes such as leaf folding, cell wall folding and vacuole fragmentation that mitigate desiccation stress, (ii) potential role of sclerenchymatous tissue within leaf folding and radiation protection, (iii) retention of ~70% chlorophyll in the desiccated state, (iv) early response of photosynthesis to dehydration by 50% reduction and ceasing completely at 80 and 70% relative water content, respectively, (v) a sharp increase in electrolyte leakage during dehydration, and (vi) confirmation of membrane integrity throughout desiccation and rehydration. Taken together, these results demonstrate that T. loliiformis implements a range of structural and physiological mechanisms that minimise mechanical, oxidative and irradiation stress. These results provide powerful insights into tolerance mechanisms for potential utilisation in the enhancement of stress-tolerance in crop plants.

Growth dependence of ovaries of facultatively parthenocarpic eggplant in vitro on indole-3-acetic acid content

This work was undertaken to investigate the growth of tissue-cultured ovaries of facultatively parthenocarpic eggplant in vitro in relation to their indole-3-acetic acid (IAA) content. Ovaries isolated from facultatively parthenocarpic eggplant (Solanum melongena L. cv Talina) and nonparthenocarpic eggplant (S. melongena L. cv Senryo-nigo) were grown under tissue culture conditions. The ovaries of facultatively parthenocarpic eggplant grew for 40 days on hormone-free medium when sucrose concentration was 50‐70 g l ˇ1 . The growth of ovaries of non-parthenocarpic eggplant ceased after 10 days. The ovaries of facultatively parthenocarpic eggplant on the medium containing 2,3,5-triiodobenzoic acid (TIBA) did not develop at all. The levels of IAA in the ovaries of both facultatively parthenocarpic and non-parthenocarpic plants were identical at excision, but were higher in ovaries of facultatively parthenocarpic than in those of non-parthenocarpic eggplant and ovaries of facultatively parthenocarpic eggplant grown on the medium containing TIBA at 20 and 40 days after culture initiation. Our findings indicated that the growth of the ovaries of facultatively parthenocarpic eggplant is supported by the availability of endogenous IAA. # 1999 Elsevier Science B.V. All rights reserved. Scientia Horticulturae 79 (1999) 143‐150

Somatic (asexual) procedures (haploids, protoplasts, cell selection) and their applications

Publisher Summary Somatic procedures form a well-established technology that has made significant contributions to plant improvement and mass propagation in horticulture, agriculture, and to some extent in forestry, as a means of rapidly multiplying elite varieties or clone. This chapter reviews recent advances in somatic procedures and their applications, including somatic embryogenesis, haploid technologies, protoplast and somatic hybridization, and use of somatic procedures in screening and development of stress-resistant plants. These techniques can be applied to improving plants for ornamental purposes and nutritional quality, and creating unique and highly desirable plants that can meet market demand. Somatic embryogenesis has become one of the most desired pathways in the regeneration of plants via tissue culture because it bypasses the necessity of time-consuming and costly manipulation of individual explants, which is a problem with organogenesis. Two patterns of somatic embryogenesis are recognized: direct embryogenesis, where the embryo develops directly on the explant, and indirect embryogenesis, in which the embryo arises from a callus. Haploid technology is also discussed in this study, which is of significant interest for developmental and genetic research, as well as for plant breeding and biotechnology. Haploid plants are useful in understanding cellular totipotency because they develop from single male or female gametes without fertilization.

Support services for higher degree research students: a survey of three Australian universities

ABSTRACT A survey was conducted across three Australian universities to identify the types and format of support services available for higher degree research (HDR, or MA and Ph.D.) students. The services were classified with regards to availability, location and accessibility. A comparative tool was developed to help institutions categorise their services in terms of academic, administrative, social and settlement, language and miscellaneous (other) supports. All three universities showed similarities in the type of academic support services offered, while differing in social and settlement and language support services in terms of the location and the level of accessibility of these services. The study also examined the specific support services available for culturally and linguistically diverse (CALD) students. The three universities differed in their emphases in catering to CALD needs, with their allocation of resources reflecting these differences. The organisation of these services within the universities was further assessed to determine possible factors that may influence the effective delivery of these services, by considering HDR and CALD student specific issues. The findings and tools developed by this study may be useful to HDR supervisors and university administrators in identifying key support services to better improve outcomes for the HDR students and universities.