Abstract
Nicotinamide adenine dinucleotide (NAD) coenzyme is abundant in pollen grain compared to the other inflorescent tissues of Arabidopsis. Pollen lacking a key NAD biosynthetic gene, nicotinate/nicotinamide mononucleotide adenyltransferase (NMNAT), was deficient in tube growth and dormancy. Tracer experiment revealed that the nmnat pollen incompletely eliminated the HPTS-containing moisture, suggesting that nmnat pollen was un-dormant. Under high humidity environment, nmnat/+ plants had long pollen tubes inside the anthers, namely precocious pollen tube growth. Even under dehydrated condition, round pollen with bulges can be distinguished in pollen population of nmnat/+ plants. Un-dormant pollen generally remains to be metabolically active, leading to senescence acceleration. In fact, the longevity of nmnat pollen was quite shorter than that of wild type. Thus, the NAD biosynthesis is essential for acquisition of drought tolerance and transition to pollen dormancy.
