Vascular anatomy of kiwi fruit and its implications for the origin of carpels

Abstract

Kiwi fruit is of great agricultural, botanical, and economic interest. The flower of kiwi fruit has axile placentation, which is typical for Actinidiaceae. Axile placentation is thought derived through fusion of conduplicate carpels with marginal placentation according to the traditional doctrine. Recent progress in angiosperm systematics has refuted this traditional doctrine and placed ANITA clade rather than Magnoliaceae as the basalmost clade. However, the former traditional doctrine stays in the classrooms as the only teachable theory for the origin of carpels. To test the validity of this doctrine, we performed anatomical study on kiwi fruit. Our study indicates that the placenta has a vascular system independent of that of the ovary wall, the ovules/seeds are attached to the placenta that is a continuation of floral axis enclosed by the lateral appendages that constitute the ovary wall, and there are some amphicribral bundles in the center of placenta and numerous amphicribral bundles supplying ovules/seeds in kiwi fruit. The amphicribral vascular bundles supplying the ovules/seeds are comparable to those usually seen in branches, but not comparable to those seen in leaves or their derivatives. This comparison indicates that the placenta in kiwi fruit cannot be derived from the fusion of collateral ventral bundles of conduplicate carpels, as suggested by traditional doctrine. Instead the vascular organization in placenta of kiwi suggests that the placenta is a shoot apex-bearing ovules/seeds laterally. This conclusion is in line with the recently raised Unifying Theory, in which the placenta is taken as an ovule-bearing branch independent of the ovary wall (carpel in strict sense). Similar vascular organization in placenta has been seen in numerous isolated taxa besides kiwi fruit. Therefore whether such a pattern is applicable for other angiosperms is an interesting question awaiting answering.

Dianthus chinensis L.: The Structural Difference between Vascular Bundles in the Placenta and Ovary Wall Suggests Their Different Origin

“…Therefore, structurally, the placenta may be an independent unique organ without any connection with other parts of the ovary wall. This conclusion is consistent with the findings of Guo et al ( 2013 ) and Wang et al ( 2015 ).…”

“…This inconformity between traditional opinions and the present result is not confined to D. chinensis . Numerous taxa of angiosperms have been reported to support amphicribral vascular bundles in placenta, including Papaveraceae (Kapoor, 1973 , 1995 ), Leguminosae (Lersten and Don, 1966 ), Winteraceae (Tucker, 1975 ), Solanaceae (Dave et al, 1981 ; Wang et al, 2015 ), Gesneriaceae (Wang and Pan, 1998 ), Buxaceae (Von Balthazar and Endress, 2002 ), Annonaceae (Endress and Armstrong, 2011 ), Actinidiaceae (Guo et al, 2013 ), and Magnoliaceae (Liu et al, 2014 ; Wang et al, 2015 ), etc. These taxa cover the whole scope of angiosperms from the basal clade magnoliids to the terminal eudicot lineage in the phylogenetic tree (Angiosperm Phylogeny Group, 2009 ).…”

“…The vascular bundle has different origin and structure in the placenta and ovary wall of angiosperm, corresponding to a shoot and a leafy organ. In kiwi fruit with axile placenta, the axile placenta is independent of the surrounding ovary wall, and the vascular bundles in the placenta are amphicribral, collateral at least in the upper part of the ovary wall (Guo et al, 2013 ). In the flowers of Magnolia , the carpel with marginal placenta is composed of two mutually independent primordia (corresponding to the ovary wall and axilla placenta).…”

Two-centre comparative experimental study of biparametric MRI at 3.0 T with and without endorectal coil using kiwifruit (Actinidia deliciosa) as a phantom for human prostate

“…Fifth, axial cross-sectional anatomy is concentric in kiwifruits but eccentric in human prostates. However, both feature zonal anatomy, with the OP and PP of kiwifruits resembling the PZ and TZ of human prostates, respectively [14, 26, 27]. Also, SNR levels were roughly similar in kiwifruits and human prostates in all sequences at both sites.…”

Kiwifruit, a botany, chemical and sensory approach a review

“…B -Longitudinal mid-cross section of fruit, showing many carpel's around the axile placenta. C-Transversal mid-section of fruit: CP, central placenta; PP, peripheral placenta; OP, outer pericarp 22.…”