Receptor‐Independent Sporopollenin

Abstract

Pollen of some species of the genus Quercus shows rod-shaped substructures in fresh or acetolysed exines, while in other species rod substructure is mostly masked by sporopollenin. Oxidation with potassium permanganate removes exine substance (sporopollenin) from between the rod substructures. We propose that the rods include receptors for sporopollenin. The sporopollenin between rods we refer to as 'receptor-independent sporopollenin'.Pollen of Typha, when mature, has tectal surfaces with concave tops and sides, whereas during development the tectal surfaces are smoothly rounded. After acetolysis treatment followed by potassium permanganate the tectum surfaces again appear rounded. When these exines are subsequently eroded by a fast atom source, rod-shaped substructures are seen to protrude from the tectum. These structures are equivalent in size and shape to the rods of the exine of Quercus.Sporopollenin that accumulates over and masks rod substrucutre is less resistant to our degradative methods than the sporopollenin in rod structures of exines. We suggest that the exine material we call "receptor-independent sporopollenin" be given a simple positive name, such as masking-sporopollenin or abbreviated to masking-spn.

Structure of the exine ofEpilobium angustifolium(Onagraceae)

“…Our findings concerning the rod-like structure of the ectexine of E. arzgzrsfifoliirriz pollen agree with Hesse's (1984) model of the structure of Epilobiiitiz exine and the results of Skvarla et al (1978) and Patel et al (1984) on the attachment of its viscin threads to the exine. There is a similarity between the unit structures described in this report and the rod-like structures of exines of Artetiiisia (Rowley et al 1981); of Befiila (Dunbar & Rowley 1984, Claugher & Rowley 1987; of Epilobiirrii (Rowley 1988); of Fagiis (Claugher & Rowley 1990); Ecliiriops (Blackmore 1990), and Qiicrciis (Rowley and Claugher 1991). Keri and Zetter's (1992) We suggest that the mostly hollow core of exine units in mature pollen of Epilobizini is due to an absence of the secondarily accumulated sporopollenin that fills in exine units in many taxa of flowering plants other than Onagraceae.…”

“…1 and 5. If "receptor independent sporopollenin" (Rowley and Claugher 1991) filled in the space around exine units in Fig. 5 and also the outer part of the exine, then there would be solid appearing columellae, about a micrometer in diameter, and a thick and solid tectum.…”

Sporoderm development and substructure inMagnolia sieboldiiand other Magnoliaceae: an interpretation

“…So-called normal cylindrical micelles have a hydrophobic liquid-hydrocarbon core and hydrophilic sheath, which causes dark-contrasted cores and moderatecontrasted sheaths in tuft-micelles ( Figure 8B, S). The phenomenon of initial dark-staining of the glycocalyx units' core with lighter periphery to lighter cores with darker binder later in development is called stain reversal, first described by Rowley and co-authors (Dunbar & Rowley, 1984;Rowley, 1987Rowley, -1988Rowley & Claugher, 1991; and later also found in other species Ǟ Figure 7. Specific plastids, typical for Magnoliaceae microspores.…”

“…The early model of Rowley and Flynn (1968) had been worked out for decades in many studies using different methods (Gabarayeva et al, 2009a). The most important milestones of John Rowley's work involve his accounts on the fundamental substructure of the pollen exine (Rowley, 1990;Rowley et al, 1995), substructure within the endexine (Rowley, 1987(Rowley, -1988, sporopollenin receptors (Skvarla & Rowley, 1987) and two types of sporopollenin: Receptor-dependent and receptor-independent as introduced by Skvarla and Rowley (1987) and Rowley and Claugher (1991). The main ideas of Rowley and his coauthors are that the exine substructure is universal for pteridophyta, gymnosperms and angiosperms and is characterised by tubule-like units, consisting of core and binder subunits so-called 'tufts', and that these units are functionally plasmodesmata-like and are capable of transferring substances/nutrients from the sporangium/anther loculus into the developing spores/microspores (Rowley & Dunbar, 1970;Rowley et al, 2003).…”

Experimental modelling of exine-like structures

“…According to Skvarla and Rowley (1987) and Rowley and Claugher (1991), early SP accumulation in the tetrad period is connected with SP-acceptor particles (SAPs). SAPs probably include enzyme molecules for SP polymerisation (Gabarayeva, 1993;Rowley et al, 1999) or they are centres of SP nucleation (Gabarayeva & Hemsley, 2006).…”