Plants on the prowl

Plants are not noted for their dynamic lifestyles. Indeed, rooted in the soil as they tend to be, they are usually written off as little more than ‘stick in the muds’. But their sedentary lifestyle is not always so sedentary; plants can travel great distances. With the obvious exception of tumbleweeds, plants are adept at recruiting other ‘agencies’ to give them a helping hand to spread far and wide, as some recent researches reveal. Technically, tumbleweeds are ‘diaspores’, which pleasingly and semantically gets us to diaspora – ‘dispersal’ – of plants, the subject of this contribution. First, hygrochasy: dehiscence that occurs upon wetting is a particularly dramatic example of exploitation of an abiotic factor to spread the genes. Although widely believed to be an adaptation to dry environments, Gedsien Pufal and colleagues have extended that notion to the alpine habitat of New Zealand (American Journal of Botany 97: 1413–1423, 2010). Investigating 23 Veronica spp., they identified hygrochasy in ten and propose that it provides an effective seed-dispersal mechanism for the solitary capsules embedded in cushion plants and helps to restrict dispersal within established habitat patches. With a related water theme we have the intriguing relationship between a frugivorous fish – Colossoma macropomum – and icythochorous plants of Amazonia (increasing your word power or what!). The fish enter the flood plains of the world’s longest river (that flows into the Atlantic Ocean…) and consume ‘massive quantities of fallen fruits and egest viable seeds’, according to Jill Anderson et al. (Proceedings of the Royal Society B; doi:10.1098/rspb.2011.0155). Recording a maximum dispersal distance of 5495 m, it is likely that the fish play a major role in seed-spread of several species in this aquatic habitat. However, the fish is over-fished, which may disrupt this ancient co-evolutionary relationship with knock-on effects to this weird and wonderful watery world. However, as impressive as those water transport figures are, the long-distance record probably has to go to air travel. Although stretching the definition of plant movement to its limit, work by Juan José Robledo-Arnuncio (New Phytologist 190: 222–233, 2011) shows that pollen from Pinus sylvestris can travel an impressive 100 km (and maybe more…). Which is good news for ‘normal’ plants, but what about the concerns of those who fear pollen from GM plants might ‘escape’ and contaminate non-GM neighbours? Well, good news from Yasuyuki Yoshimura (Journal of Plant Research 124: 109–114, 2011), who concluded that airborne pollen from GM soya was minimal and any released was restricted to a small area around the plants. Unfortunately, soya is not wind-pollinated, so the jury is probably still out in the case of anemophilous crops such as cereals. Finally, and taking plant movement to anthropomorphic extremes, there is the intriguingly entitled ‘walking cactus’ (http://www.physorg.com/news/2011-02-cactus-rewrites-arthropod-odyssey.html). Sadly, it’s not a bipedal botanic but a nickname for a recently discovered animal believed to be the closest-known fossil relative to modern arthropods. So we can’t say any more about it here…