double) in world grain yields since 1960. This is the so-called green revolution, one of the 20th century’s
greatest technological achievements [95].
The phrase green revolution was introduced by U.S. Agency for International Development admin-
istrator W.S. Gaud in 1968 [96]. The green revolution originated from the success of the American
breeder Dr. Norman Borlaug’s work on wheat in Mexico in the period 1961–1965 [97]. He was awarded
the Nobel Peace Prize in 1970 owing to his great contribution [98]. The release of the first high-yielding
modern rice cultivar IR8, a semiwarf one with erect leaves and high harvest index, by the International
Rice Research Institute in 1966 marked the start of the green revolution in Asia [99]. Around the green
revolution two major breakthroughs in rice breeding occurred in China. One was the wide distribution of
fertilizer-responsive, lodging-resistant dwarf rice varieties with high-yielding potential 2 years before the
release of IR8. Another was the commercialization of hybrid rice production in 1976 [100]. The great con-
tribution to rice breeding of academician L.-P. Yuan et al. [101] made China the first country to com-
mercialize the production of hybrid rice. Rice hybrids have a yield advantage of about 15% over the best
inbred varieties, and approximately 50% of the rice area has been devoted to plant rice hybrids in China.
Apart from seeds of high-yielding varieties, the green revolution also needs the support of adequate
amounts of chemical fertilizers, water, pesticides, improved farm equipment, etc. If all or most of them
are not available, there is no guarantee of the revolution [102]. The green revolution, in fact, is only a ce-
real revolution. Other agricultural crops have not shown any boost increase in yield [103]. In the revolu-
tion, agricultural scientists concentrated their efforts only on yield so that those high-yielding varieties
were often susceptible to various diseases and pests and had a low protein content [96,104].
B. Second Green Revolution
The achievement of the first green revolution is great, yet its shortcomings are also obvious. In addition
to those already mentioned, one of the more important ones is that only the short stalk, erect leaves in-
creasing the light utilization of the canopy and a high harvest index were emphasized, but the photosyn-
thetic efficiency of the leaf was not considered an important selection criterion for high-yielding varieties.
The potential for improving stalk height, leaf angle, and harvest index has been exploited to a fuller ex-
tent; thus, the rest room has been very limited (mainly for wheat and rice). The measures adopted in the
first green revolution, such as improved crop management and increased inputs of water, chemical fertil-
izers, and pesticides, have lost their edge in increasing crop yield. Agricultural scientists have begun to
seek a new revolution [95].
It was considered that to usher in a second green revolution, the following research topics should
be urgently addressed: increase of potential leaf photosynthesis and canopy photosynthesis, enlarge-
ment of sink capacity for assimilates, and knowledge of photosynthetic criteria for environmental stress
tolerance [105]. It appears that improving photosynthesis is a great hope of the future of agriculture
[95]. On the basis of an analysis of rice production constraints in China, it was pointed out that of the
11 plant-related factors, the most important ones are plant structure, photosynthetic efficiency, and
growth duration; therefore, research should concentrate on improving them [100]. It is increasingly re-
alized that the yield potential of varieties will be increased by improving their photosynthetic effi-
ciency. This can be possible mainly by way of DNA transfers through genetic engineering and ex-
ploitation of hybrid vigor [106]. Large benefits would result from concentrating research funds on
increasing the biological efficiency of crops. This would come from success in pursuing hybrid crops
with desirable traits such as improved plant capacity to generate photosynthates and to store them in
the grain. Moreover, scientists clearly expect biotechnology—the modern techniques for genetic trans-
fers—to provide large gains [107].
Indeed, some genetic engineers have aimed at enhancing crop photosynthesis [108]. In genetic engi-
neering, Rubisco is the most important target because it is a key enzyme in photosynthetic carbon assim-
ilation. Also, it is an enzyme with two functions, catalyzing both carboxylation and oxygenation of RuBP.
It is not only the world’s most abundant protein but also the world’s most incompetent enzyme. Under
normal air conditions, the carboxylation reaction catalyzed by the enzyme is the main rate-limiting step
in the whole photosynthesis process [109]. Natural variation in the kinetic properties of the enzyme sug-
gests that it is possible to alter the enzyme to favor the carboxylation activity relative to oxygenation
[110]. Ultimately, the desire is to engineer higher plant Rubisco to increase specificity, i.e., to favor car-
boxylation and increase photosynthetic rate and thus plant yield [111]. Exploitation of the natural biodi-
828 XU AND SHEN