Sci­en­tists hack sur­vival

East African Business Week - - LIVING -

Speed­ing up a plant’s re­sponse to fluc­tu­a­tions in light in­ten­sity can en­hance its pho­to­syn­thetic yield, ac­cord­ing to a pa­per pub­lished last week in Sci­ence.

The au­thors, who ge­net­i­cally en­gi­neered to­bacco plants to re­act more rapidly to sud­den switches be­tween light and shade, report an ap­prox­i­mately 15% im­prove­ment in the mod­i­fied plants’ pro­duc­tiv­ity.

“The pa­per is a re­ally very nice break­through. It’s the first in­stance where it has been pos­si­ble to demon­strate that, by im­prov­ing the ef­fi­ciency of pho­to­syn­the­sis, there is an in­crease in yield un­der field con­di­tions,” said plant sci­en­tist Chris­tine Foyer of the Univer­sity of Leeds, UK

“I would say it’s a game-changer,” she said.

The United Na­tions’ Food and Agri­cul­ture Or­ga­ni­za­tion has pre­dicted that by 2050 the world will need to pro­duce 70 % more food than it does cur­rently. Along with im­prov­ing stor­age, trans­port, and preser­va­tion of foods to min­i­mize losses, in­creas­ing the yields of crops is seen as a pri­mary way to in­sure against food short­ages, said Stephen Long of the Univer­sity of Illi­nois, who led the Foyer said it’s a game-changer

new re­search.

The prob­lem is, “there’s been al­most a plateau in many crops in terms of the yield in­creases us­ing cur­rent breed­ing tech­nolo­gies,” said

Foyer. “It was clear that we had to use a new ap­proach.”

Pho­to­syn­the­sis—the con­ver­sion of sun­light en­ergy into biomass—is one of the old­est bi­o­log­i­cal pro­cesses on Earth, and is ar­guably “the most im­por­tant,” said Long. In­deed, it cre­ates the planet’s oxy­gen, as well as food. Be­cause evo­lu­tion has been shap­ing pho­to­syn­the­sis for so long, “there has been a lot of skep­ti­cism as to whether [tweak­ing] it can do any­thing for crops,” Long said.

But “if you re­ally get in and drill down into the process of pho­to­syn­the­sis, you see a lot of places where the sys­tem is not as ef­fi­cient as it might be,” said Robert Blanken­ship, a pho­to­syn­the­sis re­searcher at Wash­ing­ton Univer­sity in St. Louis. Af­ter all, he added, “evo­lu­tion doesn’t make things per­fect, it just makes them good enough to sur­vive.”

One ex­am­ple of such less-thanper­fect ef­fi­ciency is a process called non­pho­to­chem­i­cal quench­ing (NPQ), a mech­a­nism that pro­tects plants from the dam­ag­ing ef­fects of overly in­tense light. Specif­i­cally, NPQ dis­si­pates ex­ces­sive light ex­ci­ta­tion en­ergy as heat to pre­vent the overex­ci­ta­tion and de­struc­tion of an­tenna com­plexes—chloro­phyll-con­tain­ing, light-re­spon­sive struc­tures crit­i­cal to pho­to­syn­the­sis. But, when light in­ten­sity drops, ex­plained Long (when a cloud cov­ers the sun, or when one leaf shades an­other, for ex­am­ple), NPQ is slow to switch off. This means that ex­ci­ta­tion en­ergy con­tin­ues to be di­verted even when not in ex­cess. Com­puter mod­el­ing has shown that this lag could re­duce a plant’s po­ten­tial car­bon up­take by “any­thing be­tween eight and 40 per­cent,” said Long.

Long and col­leagues thus planned to in­crease the speed with which NPQ switches on and off. To do this, they over-ex­pressed in to­bacco plants the three main genes con­trol­ling NPQ: two en­cod­ing the en­zymes vi­o­lax­an­thin de-epox­i­dase and zeax­an­thin epox­i­dase, and one en­cod­ing the pro­tein Psbs—a sub­unit of the pho­to­sys­tem II an­tenna com­plex.

The team used to­bacco be­cause it is a tech­ni­cally amenable crop, said Long, ex­plain­ing that food crops such as rice, soy, and cas­sava, would be the ul­ti­mate tar­gets.

Us­ing real time mea­sure­ments of NPQ re­sponse speed (by chloro­phyll flu­o­res­cence anal­y­sis) and of car­bon diox­ide up­take (by in­frared gas anal­y­sis), the team ob­served that both pro­cesses were sig­nif­i­cantly in­creased. And these im­prove­ments trans­lated to a 14% to 20% in­crease in dry weight per plant in field con­di­tions.

“It’s im­pres­sive what they did,” said Blanken­ship, ad­ding that “there are a lot of other ways [to tweak pho­to­syn­the­sis] that might pos­si­bly have even big­ger im­pacts,” such as ex­pand­ing the spec­trum of light that plants can use.

In­deed, agreed Foyer, “there are many steps along the process of pho­to­syn­the­sis where it is pos­si­ble to see that im­prove­ments could be made to in­crease yield. And what Steve Long and his col­leagues have done is to tackle just one.”

With this ad­vance, she added, “the 70 to 100 per­cent in­crease in yield that we des­per­ately need by 2050 is look­ing much more like a reality now.

Agen­cies

The team used to­bacco be­cause it is a tech­ni­cally amenable crop, said Long, ex­plain­ing that food crops such as rice, soy, and cas­sava, would be the ul­ti­mate tar­gets

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