부산대학교 도서관

This study explored the uptake, accumulation and translocation of phosphorus (P) in cereals in support of more sustainable management of this critical and finite nutrient. A pot experiment evaluated two low phytate (lpa 1-1 and lpa M955) and two normal phytate (Harrington and Sanette) cultivars of spring barley with total seed P concentrations of 3.4mg g-1, 6.1mg g-1, 4.3 mg g-1 and 4.4 mg g-1 respectively and their growth response under Soil P Index 1 with and without added P. The lpa lines yielded as well as normal phytate barley and even better under P-limiting conditions. The lpa barley cultivars lpa1-1 and lpa M955 had 17% and 15% less total plant P uptake on average compared to Harrington and 22% and 20% less compared to Sanette respectively at harvesting. Among all four cultivars, lpa1-1 had the lowest seed total P concentration by 23%, 30% and 14% compared to lpa M955, Harrington and Sanette respectively due to lower P translocation to the grain, both with and without added nutrient P. Both lpa 1-1 and lpa M955 however, had significantly lower seed phytic acid concentration ranging between 50%-90% lower than Harrington and Sanette but the mineral elements content was unaffected by the reduction in seed phytic acid. Cultivar response under varying soil P environments (Index1, 2 and3) with and without added nutrient P was investigated. Soil P Index 1 had the highest response to added nutrient P resulting in 42%, 47%, 37% and 26% increase in total plant P uptake in lpa 1-1, lpa M955, Harrington and Sanette respectively. An average of all four cultivars showed P addition increased total plant P uptake by 38% (Index 1), 15% (Index 2) and 11% (Index 3) while total plant dry weight increased by 22%, 9% and 3% under soil P Index 1, 2 and 3 respectively. All four cultivars showed no significant total plant dry weight increase at soil P Indices 2 and 3 as a result of added nutrient P confirming current fertilizer recommendation systems. A higher soil P environment (Index 3) resulted in an unnecessary increase in total plant P uptake, seed total P concentration as well as seed phytic acid concentration in all cultivars despite no significant increase in total plant dry weight. Both lpa1-1 and lpa M955 translocated an average of 10% less plant P to the seed than Harrington and Sanette under soil P Index 1 and 2. lpa 1-1 had the lowest total plant P uptake among all four cultivars under varying soil P environments ranging between 9%-28% lower than lpa M955, 13%-25% lower than Harrington and 7%-28% lower than Sanette. Despite this, all four cultivars had no significant differences in total plant dry weight and consequent grain yield confirming that lpa 1-1 utilizes less P to achieve similar plant yield to normal phytate barley (Harrington and Sanette). A mutagenized lpa 1-1 population of 3119 lines was screened for further reductions in seed total P concentration compared to lpa 1-1 and the parent Harrington. The M3 population had seed total P concentrations ranging from 1.7 to 4.7mg g-1 with >90% being lower than 3.7 mg g-1. Selection of 220 reduced seed total P concentration lines produced an M4 population with < 3.4 mg g-1 seed total P concentration. Three M4 lines with 30% seed total P concentration reduction compared to lpa 1-1 were screened in a pot experiment under soil P Index 1 both with and without added nutrient P. Like lpa 1-1, they performed and yielded the equally as well as Harrington but with lower total plant P uptake, however, they showed even further reductions in seed total P concentration (3.0-3.4mg g-1) and consequently lower phytic acid (0.15 -0.18 mg/100g). This suggests that the low phytate trait is heritable and that it is possible to further reduce seed total P concentration and subsequent total plant P uptake without affecting the yield. The gene that most likely mutated in lpa 1-1 resulting in reduced seed total P concentration is a sulfate transporter gene, HvST. Using the CRISPR/Cas9 gene editing tool to specifically target HvST in Golden Promise barley, 11 potential mutants were identified in the T0 generation. Grains from six T0 lines were phenotyped and all showed 40% lower seed total P concentration compared to Golden Promise. This confirmed that HvST is the gene responsible for the low seed total P concentration. Wheat homologues of HvST were also identified using BLAST (basic local alignment search tool) and 13 wheat TILLING lines having variation in this sequence were selected. Genotyping of their progeny identified variations in target alleles corresponding to the HvST gene. Phenotyping is needed to detect whether these wheat lines display a low phytate trait. There is potential for breeding the low phytate trait into high yielding commercial cereals to develop low P cultivars without a yield penalty. The findings suggest that inorganic P fertilizers can be used more efficiently thereby reducing water pollution and improving human and animal nutrition.