Gene flow occurs with a noticeable frequency from cultivated rice to its weedy and wild relatives, and this might cause potential ecological consequences. It is recommended that isolation zones should be established with sufficient distances between GM rice varieties and wild rice populations to avoid potential outcrosses. Also, GM rice should not be released when it has inserted genes that can significantly enhance the ecological fitness of weedy rice in regions where weedy rice is already abundant and causing great problems.

The tapetum plays a crucial role in pollen development. This secretory tissue produces numerous nutritive proteins necessary for pollen maturation. The tapetum, whose cells undergo programmed cell death (PCD), is completely diminished by the time the pollen is fully mature. Our previous studies on a thermosensitive genic male-sterile (TGMS) rice (Oryza sativa L.) suggested that male-sterility was due to failure in pollen development. In this paper we describe how further analysis of the TGMS rice revealed that male-sterility is associated with premature PCD of the tapetum. Cytological observations of TGMS rice anthers at various developmental stages indicated that PCD initiates at an early stage of pollen development and continues until the tapetal cells are completely degraded, resulting in pollen collapse. Transmission electron microscopy showed the morphologically distinct hallmarks of apoptosis, including cytoplasmic shrinkage, membrane blebbing, and vacuolation. Identification of DNA fragmentation using the TUNEL assay supports the hypothesis that premature PCD is associated with male-sterility in the rice. The tissue-specific feature of the thermosensitive genic male-sterile phenotype is discussed with regard to PCD during anther development.

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Pb inhibits plant growth. To study Pb tolerance in rice (Oryza sativa), we screened 229 varieties for Pb tolerance or sensitivity. Three-day-old seedlings were treated for 12 d with 20 m Pb solution. Based on the dry weight of the root, three var Kumnung) and three Pb-sensitive (var Aixueru, var C-9491, var Milyang23) rice varieties were selected. The root biomasses of the tolerant varieties were approximately 10-fold higher than those of the sensitive ones. The greatest morphological difference between the two groups was in the growth of the adventitious roots, as tolerant lines were able to develop adventitious roots after 6 d of Pb treatment, whereas sensitive ones did not develop any even after 15 d. The growth of adventitious roots in the tolerant varieties was dependent on a mechanism, whereby Pb was altered to a form that cannot be taken up by the tissue, because (a) the solution in which the tolerant varieties of rice had grown still contained Pb but nevertheless did not affect the root growth of new rice seedlings, and (b) the adventitious roots of tolerant seedlings developed in Pb solution contained little Pb. The oxalate content in the root and root exudate increased upon Pb treatment in the tolerant varieties, whereas the opposite was observed for the sensitive ones. Oxalate added to the growth solution ameliorated the inhibition of root growth by Pb. These results suggest that compounds such as oxalate secreted from the root may reduce the bio-availability of Pb, and that this may constitute an important Pb tolerance mechanism in the tolerant rice varieties studied here.

Weedy rice refers to the unwanted plants of the genus Oryza that have some undesirable agronomic traits and pose a major threat to sustainable rice production worldwide. Widespread adoption of direct seeded rice and hybridization or gene flow between cultivated rice and their wild relatives has resulted in the creation and dissemination of weedy rice. Currently, weedy rice (Oryza sativa f. spontanea) has become one of the most common weeds infesting rice fields worldwide. In this paper, we review the biology, physiology, evolution, and genetic features of weedy rice. We also discuss the major obstacles in weedy rice management, including high diversity of weedy rice, ecological impacts of gene flow on weedy rice, changing climate, and weedy rice management. We then present a framework for the sustainable management and utilization of weedy rice. Our main emphasis is to explore the reservoir of natural variations in weedy germplasm and to utilize them for crop improvement. This review outlines some of the latest biotechnological tools to dissect the genetic backgrounds of several favorable traits of weedy rice that may prove beneficial for breeding and evolutionary studies on cultivated rice. We suggest that by merging the disciplines of genomics, breeding, and weed management, we can achieve the goal of sustainable rice production.