Abstract
Phosphorus (P), an element required for plant growth, fruit set, fruit development, and fruit ripening, can be deficient or unavailable in agricultural soils. Previously, it was shown that over-expression of a proton-pyrophosphatase gene AVP1/AVP1D (AVP1DOX) in Arabidopsis, rice, and tomato resulted in the enhancement of root branching and overall mass with the result of increased mineral P acquisition. However, although AVP1 over-expression also increased shoot biomass in Arabidopsis, this effect was not observed in tomato under phosphate-sufficient conditions. AVP1DOX tomato plants exhibited increased rootward auxin transport and root acidification compared with control plants. AVP1DOX tomato plants were analysed in detail under limiting P conditions in greenhouse and field trials. AVP1DOX plants produced 25% (P=0.001) more marketable ripened fruit per plant under P-deficient conditions compared with the controls. Further, under low phosphate conditions, AVP1DOX plants displayed increased phosphate transport from leaf (source) to fruit (sink) compared to controls. AVP1DOX plants also showed an 11% increase in transplant survival (P<0.01) in both greenhouse and field trials compared with the control plants. These results suggest that selection of tomato cultivars for increased proton pyrophosphatase gene expression could be useful when selecting for cultivars to be grown on marginal soils.
Highlights
The essential macronutrient phosphorus (P) is relatively unavailable to plants in many soils when present as calcium salts or iron–aluminum oxide complexes (Holford, 1997)
Similar results were observed in root acidification and auxin transport in AVP1DOX tomato seedlings (Fig. 1A)
Enhanced auxin transport in AVP1DOX provided the explanation for larger roots measured in transgenic tomato plants
Summary
The essential macronutrient phosphorus (P) is relatively unavailable to plants in many soils when present as calcium salts or iron–aluminum oxide complexes (Holford, 1997). Tomatoes grown in soils with low phosphorus availability manifest deficiency symptoms such as stunting and leaf darkening before flowering and almost always exhibit reduced fruit size and production (Havlin et al, 2005). For this reason, fertilization of tomato crops with P just before fruit set is a standard component of cultivation practices (Egel et al, 2008). Over-expression of the proton-pyrophosphatase in Arabidopsis, rice, tomato, and maize was reported to enhance P utilization (Yang et al, 2007; Pei et al, 2012). The loss or the reduction of proton-pyrophosphatase AVP1 function in Arabidopsis results in reduced shoot and root growth (Li et al, 2005, Ferjani et al, 2011)
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