e-journal

Spatial patterns of photosynthesis in thin- and thick-leaved epiphytic orchids: unravelling C3–CAM plasticity in an organ-compartmented way

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† Background and Aims:
A positive correlation between tissue thickness and crassulacean acid metabolism (CAM) expression has been frequently suggested. Therefore, this study addressed the question of whether water availability
modulates photosynthetic plasticity in different organs of two epiphytic orchids with distinct leaf thickness.

† Methods:
Tissue morphologyand photosyntheticmode(C3 and/orCAM)were examined in leaves, pseudobulbs and roots of a thick-leaved (Cattleyawalkeriana) and a thin-leaved (Oncidium ‘Aloha’) epiphytic orchid. Morphological
features were studied comparing the drought-induced physiological responses observed in each organ after 30 d of either drought or well-watered treatments.

† Key Results:
Cattleyawalkeriana, which is considered aconstitutiveCAMorchid, displayed a clear drought-induced up-regulation of CAM in its thick leaves but not in its non-leaf organs (pseudobulbs and roots). The set of morphological traits of Cattleya leaves suggested the drought-inducible CAMup-regulation as a possible mechanism of increasing water-use efficiency and carbon economy. Conversely, although belonging to an orchid genus classically considered as performing C3 photosynthesis, Oncidium ‘Aloha’ under drought seemed to express facultative CAMin its roots and pseudobulbs but not in its leaves, indicating that such photosynthetic responses might compensate for the lack of capacity to perform CAMin its thin leaves. Morphological features of Oncidium leaves also indicated lower efficiency in preventing water and CO2 losses, while aerenchyma ducts connecting pseudobulbs and leaves suggested a compartmentalized mechanism of nighttime carboxylation via phosphoenolpyruvate carboxylase (PEPC) (pseudobulbs) and daytime carboxylation via Rubisco (leaves) in drought-exposed Oncidium plants.

†Conclusions:
Water availability modulated CAM expression in an organ-compartmented manner in both orchids studied. As distinct regions of the same orchid could perform different photosynthetic pathways and variable degrees of CAM expression depending on the water availability, more attention should be addressed to this in future studies concerning the abundance of CAM plants.

Key words: Cattleya walkeriana, crassulacean acid metabolism, drought, epiphytic orchid, leaf succulence,
non-leaf photosynthesis, Oncidium ‘Aloha’, photosynthetic plasticity.

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Informasi Detail

Judul Seri

Annals of Botany

No. Panggil

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Penerbit

Oxford : Oxford University Press on behalf of the Annals of Botany Company., 2013

Deskripsi Fisik

Annals of Botany 112: 17–29, 2013

Bahasa

English

ISBN/ISSN

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Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

112:2013

Subjek

EKOFISIOLOGI TANAMAN

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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