Daily Archives: 10th of February 2013

Making more orchids

Spathoglottis plicata Spathoglottis plicata is a terrestrial orchid species that is sold commercially by many growers. Orchids are slow to propagete, and for commercial success, many species rely on micropropagation. Although this is a common method these days, much of the science behind regeneration of whole plants from tiny specks of plant tissue remains uncertain.

This paper describes the impact of auxin distribution on the initiation of first leaves and the effect of exogenous auxin application on the formation of trichomes and propagative structures in S. plicata seedlings at three stages of development.

 

Novak, S.D., & Whitehouse, G.A. (2013) Auxin regulates first leaf development and promotes the formation of protocorm trichomes and rhizome-like structures in developing seedlings of Spathoglottis plicata (Orchidaceae). AoB Plants.
Auxin flows in a polar manner to target tissues and exert its morphogenic effect. Preventing auxin movement, with polar auxin transport (PAT) inhibitors, or increasing auxin levels in tissues through exogenous application can provide a means for assessing the importance of appropriate tissue distribution and concentration of this hormone during development. The formulation of culture media for micropropagation has been the primary focus of most orchid tissue culture research, a goal that unveils seedling hormone responses at a single point in development. This study was unique because it evaluated the auxin response of orchids during three stages of seedling development. Seedlings were grown on standard culture media for 10, 35 and 85 days. Each group was sub-cultured onto auxin- and/or PAT inhibitor-containing media for an additional 10, 30 and 60 days, respectively. Data were collected on first leaf initiation, trichome formation and the appearance of propagative structures. In the 20-day seedlings, auxins and PAT inhibitors promoted precocious formation and random placement of protocorm hairs rather than in tufts, as seen in older, control seedlings. The 65-day seedlings formed protocorm-like bodies, rhizome-like growths from the stem, and fleshy leaves with trichomes. Seedlings cultured for 145 days developed microshoots or callus growth in the axils of older leaves and exhibited necrosis of original seedling roots and leaves. In general, exogenously applied auxin promoted the reversion of differentiated Spathoglottis plicata seedling tissue to a morphology that had propagative properties. Additionally, auxins commonly induced hair formation, which suggests that protocorm hairs may be root hair-like in nature. This work characterized three auxin growth responses in S. plicata seedlings that have not been reported in orchids: (i) the inhibition of first leaf initiation and abnormal first leaf morphology; (ii) the promotion of trichome formation; and (iii) the induction of rhizome-like structures and microshoots at a specific stage in seedling development.

Plant establishment on unirrigated green roof modules in a subtropical climate

Green roof The use of green roofs as a self-reliant and low-input technology emerged in Europe, Scandinavia and the UK, where climate conditions are favourable for maintaining green roof vegetation without irrigation. But how useful is this environmentally-friendly technology in more hostile climates?

The application of green roof technology has become more common in the central, northwestern and eastern USA, and is now being employed across the southern USA as well. However, there is little research in the literature that evaluated plant survival on unirrigated green roofs in subtropical climates that experience frequent drought and heat stress. A new paper in AoB PLANTS summarizes the results of a study of plant establishment on a modular green roof in south-central Texas. Fifteen plant species were field tested in green roof modules on a four-storey building in College Station, Texas, with irrigation limited to the first several weeks of establishment. Climate data, plant growth and species survival were measured over three growing seasons.

Green roof module

The establishment and survival of several plant species without any mortality suggests that irrigation limited to the first few weeks after planting may be an effective approach on green roofs in spite of the more challenging climatic conditions in the southern USA. Since the climate in south-central Texas had been consistently drier and warmer than normal during the study period, longer-term research on these species is recommended to expand knowledge of establishment requirements for these species under a wider range of conditions, including wetter than normal years.

Dvorak, B.D., & Volder, A. (2012) Plant establishment on unirrigated green roof modules in a subtropical climate. AoB Plants.