Abstract: In this research, ramets of Gibasis pellucida propagated from stem cuttings were used as experimental material to explore the morphological and ultrastructural changes in leaves, when grown at different light levels. Shading net was used to create a series of five light environments with 0, 25%, 50%, 75% and 95% shading, respectively. The results indicated that: with reducing light level from 0 to 75% shading, leaf length, width and area progressively increased to a maximum for the experimental material at 75% shading. Along with change in leaf size, the colors of the leaf upper surface changed from yellow-green to dark-green, and that of the leaf lower surface changed from deep-purple to light-purple. When the shading intensity was 95%, the purple color disappeared. Leaf chorophyll a, chlorophyll b, and chlorophyll (a+b) contents were negatively correlated with light intensity (P<0.05), while leaf anthocyanin content was positively correlated with light intensity. The thickness of leaves and their upper epidermis, lower epidermis, palisade tissue and spongy mesophyll tissue decreased significantly with decreasing light intensity (P<0.05), while the ratio of palisade:spongy mesophyll thickness, and tightness of tissue were highest in the 50% shade treatment. The 0 and 25% shade treatments slightly damaged the ultrastructure of mesophyll cells, causing the expansion of some thylakoid grana and stroma, and enlargement of starch grains. Extremely low-light intensity (95% shading) resulted in serious disruption to the ultrastructure of mesophyll cells, together with some chloroplast disintegration and emptying of starch grains. In summary, G. pellucida possesses a very strong shade adaptation response, and mechanisms used to adapt to the different light environments involved adjusting the shape, pigmentation and anatomical structure of leaves. While G. pellucida could survive in the extremely low light environment of the 95% shade treatment, the structure of the leaf internal organs was damaged irreversibly by this degree of shading.

Key words: light intensities, Gibasis pellucida, leaf shape, anatomical structure, ultrastructure