Tree Physiology Advance Access published online on October 13, 2009
Tree Physiology, doi:10.1093/treephys/tpp086
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Water deficit-induced changes in mesocarp cellular processes and the relationship between mesocarp and endocarp during olive fruit development
1 Dipartimento di Coltivazione e Difesa delle Specie Legnose, Università di Pisa, Via del Borghetto 80, 56124 Pisa, Italy
2 Corresponding author (rgucci{at}agr.unipi.it)
3 Dipartimento di Scienze Ambientali e delle Produzioni Vegetali, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy
4 Instituto de Agricultura Sostenible, C.S.I.C., P.O. Box 4084, 14080 Cordoba, Spain
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Abstract |
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A field experiment was conducted during two consecutive growing seasons to determine and quantify the growth response of the olive (Olea europaea L. cv. Leccino) fruit and of its component tissues to tree water status. Pre-dawn leaf water potential (
w) and fruit volume were measured at about weekly intervals, and fresh weight (FW) and dry weight (DW) of the fruit tissues at 15, 20 and 21 weeks after full bloom (AFB). Fruit anatomical sections were prepared at 8, 15 and 21 weeks AFB for area determinations and cell counts. Fruit volume of the well-watered trees (average w = –0.97 MPa) increased rapidly and reached the greatest final size, that from the most stressed (average w = –2.81 MPa) grew most slowly and were smallest. In general, equatorial transverse areas of the mesocarp increased with increasing w, and this response was more evident at 21 than at 15 weeks AFB. By 21 weeks AFB, the mesocarp of the well-watered trees reached values more than three times higher than those measured at 8 weeks AFB. The endocarp FW and DW did not increase between 15 and 21 weeks AFB. Within each sampling date the endocarp area, FW and DW responded weakly to w. The mesocarp-to-endocarp ratio (FW and DW) increased from 15 to 21 weeks AFB regardless of water status, mainly due to the mesocarp growth. In both years at 20 and 21 weeks AFB, low values of the mesocarp-to-endocarp ratio were found with w below –2.5 MPa. Within the mesocarp, cell size was more responsive to water deficit than to cell number. At 8 weeks AFB, the number of cells in the mesocarp was unaffected by tree water deficit, whereas cell size decreased, although slightly, in fruits sampled from trees in which w was < –3.0 MPa. At 21 weeks AFB, cell size showed a linear decrease with increasing level of water deficit, whereas the number of cells at 21 weeks AFB decreased as the w decreased below –2.5 MPa and seemed unaffected above that range. Overall, the results clarify the complexity of the water-induced response of mesocarp and endocarp growth and cellular processes of olive fruits.
Keywords: cell number, cell size, fruit growth, leaf water potential, Olea europaea, seed
Received July 8, 2009; Accepted September 11, 2009